You want to send an attachment with your marketing or transactional email and information so far didn’t get you anywhere, really. Now, this guide will help answer all the questions you might have about sending attachments in commercial and transactional emails.
Attachments in emails have technical limitations, but using them can increase the value and the usefulness of your emails.
In this guide:
The advantages of email attachments
When not to send attachments with your email
6 Use Cases for PDF attachments and email
Pre-rendered versus dynamic PDF attachments
How to create effective dynamic email attachments
ESPs that allow you to send PDF attachments
In some cases, you send attachments, in other cases that isn’t the smartest to help customers. This article provides insight into the ‘why’ and ‘how’ of attachments.
4 advantages of attachments in transactional email
Transactional emails are always a direct result of conversion (hence ‘transaction’). For instance, you send password reset emails when your customers forget their login details, or you send order confirmations so your customers know their orders are being handled. etc.
Sending transactional emails relies on the relationship between your recipients and your brand. These emails help your recipients, and so should your attachments. There are a few major advantages to attachments for your recipient. It allows them to for instance:
- Save content for later;
- Import data into other systems (especially .csv format);
- Edit/review/sign files in some cases;
- Share files with others.
Transactional emails are known to have the highest open rates in the email industry. The way customers engage with these emails differs from marketing emails. Whereas marketing emails aim to sell, transactional emails are vital to your client’s journey. This type of email aims to help your customer.
Let’s look into a particular type of attachment: PDF files.
Why PDF is so useful for attachments
Attachments come in shapes and sizes. Most popular email attachments are Office documents, HTML, calendar items, and PDF files. (but there are about 550 types of file extensions). PDFs have some extra advantages which make them the industry standard for email attachments:
- Are readable/zoomable on every device;
- Allow interactivity within the document;
- Have the same design, same fonts, images, margins et cetera.
- Can be in various shapes and sizes.
The PDF format is portable, it looks the same on every device. So if you open the file on mobile it has the same layout as the ones opened in native desktop view.
This makes PDF the de facto standard for exchanging content files. Whether it’s between Google Drive and iCloud or your systems and your recipient’s inbox. It is the only format that allows both the sending and the receiving party to view the file in the exact same way – even in inbox preview.
Indirectly sending attachments
In many cases, it’s better to not attach a file to your email but to link to the location of the file. To share standard PDF attachments, for instance, you can include a hyperlink in your email. With this link, the recipient can retrieve the PDF (this is often used for whitepapers).
Indirectly sending attachments is also advised when the file contains personal information, exceeds the file size limit, or when the attachment is not in PDF format.
Plus, you keep the email size small by hosting the PDF.
You can host documents on your website, a CDN, or document hosting space like Google Drive, Dropbox, OneDrive or specific a Document Management Solution (DMS) or Digital Asset Management (DAM) system.
In other circumstances (i.e. when sending monthly reports or invoices) you can refer to a file in the user’s login portal.
When not to send attachments with your email
Sending PDF files attached to your marketing emails will do more harm than good. It can harm your email deliverability. Many ESPs won’t allow it, sending emails with attachments in mass can slow down your email speed.
So you should only consider attachments for your transactional email, not marketing emails.
In some cases, sending PDF files is not the best idea, even with transactional email. PDF attachments are helpful when the email has an administrative task.
Don’t attach PDF files to transactional emails like:
- Welcome emails;
- Password reset emails;
- Two-Factor security emails;
- Notification emails.
Don’t add attachments to any emails that are sent to notify the recipient or let him do one simple task, like click a button to reset the password. This will only confuse the recipient and is a waste of their inbox space.
6 Use Cases for PDF attachments and email
By now, you’re probably wondering how you should use PDF attachments with your email. There a several best practices for emails with attachments:
- Standardized PDF attachments & downloadable content;
- Payment information;
- Order confirmations;
- Digital tickets;
- Periodical reports;
- Digital signatures & forms.
Note that all types of PDF can contain more than text and graphics. PDF allows interactive elements, layers, rich media (i.e. video content), and even 3D objects.
1. Attach a standardized PDF attachment for printing
Most PDFs sent through email are the ones that you create once and locate somewhere in your CMS or in cloud storage. You can find tons of examples in B2B as well as B2C emails.
Think of whitepapers, presentations, and eBooks. But also content like maps, pricing sheets, or route descriptions. Some attach the files to their emails, some refer to the online location of it. Either way, these types of emails typically aren’t interactive but are optimized for printing.
2. Send Payment information and invoices
Other frequently used PDF files are invoice attachments, receipts, and (business) proposals.
What they have in common is that they contain financial / payment information. Like the previous use case, these PDFs are not interactive. Since most customers will print or save these PDFs for administrative purposes, just send simple PDF files.
You need invoices to look (and be, obviously) legitimate, so make sure it does.
Add your logo, your company details et cetera. This information is required by legislation, but will also
a) make your receiver trust the email;
b) let your receiver confirm his own details;
c) make your attachment useful to their bookkeeping or invoicing software.
Yet, you should never include details that are sensitive to phishing, like credit card numbers. Instead of displaying “5115 5477 8866 3418”, hash it to “XXXX XXXX XXXX X418”.
Invoices and reminders can also be generated by Membership, Bookkeeping Accounting and Invoicing software like Freshbooks, Quickbooks, Zoho Books, Chargebee Wave, etc. The ones that also have an API, will be able to integrate the data so you can take the process from there.
3. Send order confirmation attachments with your email
eCommerce marketers will recognize order confirmations as their most opened and clicked emails. Order confirmations give your customers confidence that their order came through correctly and make it easier to find back the order information, without having to log in again.
PDFs of order confirmations often can contain images, given its function in the Customer Journey. Enriching your order confirmations with all the details your recipient needs (in text and graphics) will save you costly customer service phone calls.
Invoices and reminders can also be generated by Membership, Bookkeeping Accounting and Invoicing software like Freshbooks, Quickbooks, Zoho Books, Chargebee, Wave, etc. The ones that also have an API, will be able to integrate the data so you can take the process from there.
4. Attach Digital tickets to your transactional email
Some more advanced PDFs combine data from multiple source systems. A prime example is a digital ticket.
This type of PDF typically has a QR code, some information about the event, payment information, and order details. Unless you have a really powerful system that does it all, you probably rely on multiple systems for these data.
Digital tickets allow your customers to print and use them to enter your event, park, or building. They can also save the attachment to their phone so they’ll always have their tickets, boarding passes, et cetera on them.
5. Attach PDF reports and daily market updates to your email
A lot of B2B and B2C companies provide periodical reports to their clients. For instance, a yearly (“Your favorite songs of 2020”), monthly (“Check your progression for May”), or even daily statistics overview when opted for.
These reports require a lot of data.
Statistics are often linked to specific users and might need personalized content. Imagine you’re learning a new language and your monthly reports contain the number of courses you took and the progression you made.
The remaining content differs: You either are doing a great job, or you should put in some more effort. Another well-known example is the monthly email energy providers send out to help customers gain insight into their energy consumption.
6. Request Digital signatures & form filled with PDF attachments
The PDF format has other important features to offer, for instance:
- Digital signatures,
This enables senders to create workflows requiring these features. Digital signatures are useful when i.e. contracts (DPAs, legal, estate) are part of your automated processes.
You can use forms when someone applies for a job, needs to fill out a claim form or anything requiring quite some (personal) information. Being encrypted, PDF is a safe and easy way for the data to be shared. Recipients can just fill out the PDF, reply to the email, and trust their data is safe with you.
Pre-rendered versus dynamically generated PDF attachments
There are basically two ways to add attachments to your emails. With a trigger or along the way in the email delivery process.
What are static / pre-rendered attachments?
It’s all in the name: this type of attachment is already generated and that static PDF or file is hosted somewhere your email platform can find it.
A static PDF attachment can be a file hosted on your website, uploaded to your email platform, your DAM (Digital Asset Management tool), or a hosting provider like Google Drive. The email platform can then retrieve the PDF (triggered) and send it along with the email in an SMTP, or API process.
What are dynamically generated attachments?
Dynamically generated PDFs are generated when needed. You use a PDF template and fill it with the necessary variables. You can compare it to using an email template. The design and content blocks are there and the data is added at the moment it is ready to go!
This allows you to get more data from your source systems, the PDF will always be up to date and you create PDF attachments in your brand style.
When to use static versus dynamically generated attachments.
In the email delivery process, pre-rendered attachments are the easiest solution. You generate them once and send them attached to your email in the SMTP process. Yet sometimes, pre-rendered PDF attachments can be ugly (because of the way it is generated) and un-personalized.
Dynamic attachments are great when data needs merging or an attachment needs to be hyper-personalized. Invoices, entrance tickets, and periodical reports, for example, are great for this.
Dynamic PDF attachments can be hard to develop due to some technical details in XHTML (more on that later). So only use the dynamic PDF attachments when needed.
Ask yourself the following questions when considering the type of attachment to send:
- Is my attachment supposed to be interactive or engaging?
- Do I need data from multiple source systems to create the PDF?
- Do I need to change the way my PDFs look, add logos, variables and/or content?
If the answers to two or three of these questions are ‘yes’, you should consider dynamically generating PDFs. In some cases, you can use both pre-rendered and dynamic attachments in the same email. In the example below an adventure zoo in The Netherlands attaches both a map of the park and an entrance ticket.
How to create effective dynamic email attachments
You can create static, trigger-based PDFs yourself. Or let your CMS or invoicing system do so.
Dynamic attachments, however, require a specialized platform. This can either be in an advanced SMTP provider or a separate PDF generation platform next to your SMTP provider.
1. Collecting data from your systems
What you know about your customers isn’t always based on personal connections anymore. Every business nowadays uses various systems to gain information about their customers. What they like, what they do, what they buy. The information they leave with you, you can use to personalize your communications.
These systems each have specific information about a customer. Your invoicing system doesn’t have the same information as your social media hub and vice versa. Yet, you might want to use several bits of information about a customer in your emails or PDFs.
To create PDFs with various bits of information, you need to use so-called APIs. APIs allow you to retrieve data from multiple sources and use that data to add variables to your emails and attachments.
A CDP allows you to collect, unify, and use data from various sources.
To create dynamic PDFs, you need to first collect the needed data. Use that data to personalize your content in an XHTML template that you convert to PDF.
2. Use data to personalize content
Once you have collected the data you need, you can personalize your content. Our previous examples already showed you what personalization can do, but there’s more. Variables allow your PDFs to be unique to every recipient. Did your customer order a new pair of jeans paid by invoice? Add a link or QR code to your attachment for later payment.
3. Creating XHTML and converting it to PDF
Contrary to email templates, PDF templates are in XHTML format. This allows you to use pretty much the same variables as in email templates, but have some restrictions. For example, XHTML and CSS are not best buds and neither are margins. CSS markup in a style sheet can cause some or all of it to be ignored.
This article doesn’t aim to guide you through XHTML development, but for more background information, check O’Reilly’s website.
Picking the best provider for sending PDF attachments
Now that you know how to attach PDF files, it’s time to take a look at what email providers support PDFs. Every SMTP relay can deliver trigger-based attachments. Many providers yet lack the functionality to create dynamic PDFs. Take a look at which popular SMTP providers can and cannot send PDFs. In the table below we’ve added the five most popular Email Marketing vendors as well:
Most email marketing platforms don’t allow attachments at all to prevent spam. Or they do allow you but prefer you to host your files at i.e. Dropbox and link to them.
You’ll then need a different platform to deliver your invoices and tickets. There are several PDF generation tools, like PDFMonkey, ContractExpress, Avodocs, and DocSpring.
Frequently Asked Questions about sending PDF attachments
Q: How are PDF attachments displayed in popular inboxes?
Every email client has its own way of displaying attachments. Based on the file size, the operating system, and the client itself.
For instance, web-based Gmail shows the receiver a clear thumbnail of the attachments. Apple Mail yet tends to show the full PDF in the email itself. As most email clients display a thumbnail and its name, be sure to give your PDF attachment a proper name; ‘noname.pdf’ or ‘43j32nfhd.pdf’ is just sloppy.
Q: What is the maximum size of an attachment?
The standard maximum size of an attachment is 10MB. With an attachment this large, all email clients will accept the attachment initially. Some email clients (like Gmail and AOL) have a 25MB cap. But, when you are sending a lot of emails, try keeping your file sizes smaller (~3MB) so
a) your server won’t have a mental breakdown and
b) attachments have less impact on your email deliverability.
Q: What are the risks of sending attachments?
Be aware that email clients have spam filters that could filter out your emails at any time. Most spam filters don’t really like attachments. However, when you meet most requirements (keep a small file size, use trusted file formats), chances of being filtered are low.
Q: How do I keep track of opens & clicks in PDF?
Basically the same way you keep track of opens and clicks for regular email:
- adding a tracking pixel that sends a signal whenever the receiver opens your PDF;
- adding UTM tags to links in the PDF, so you know someone has opened and clicked the PDF.
Adding a tracking pixel, however, is a bit risky, as most PDF Readers do not communicate with the systems reading the tracking information.
Q: How do I add calendar files to transactional emails?
iCalendar is the industry standard for sending calendar items (supported by i.e. Microsoft Office 365, Apple Calendar, and Google Calendar). You can attach calendar items (.ical) to your emails in plain text or HTML. Both are attached in the same way PDFs are: either via a trigger (file is hosted somewhere) or during the SMTP process where calendar events are generated dynamically.
Q: Can ‘hackers’ intercept and change my attachments?
Like regular email, ‘hackers’ can intercept unprotected attachments. But, when you (read: your email provider) take appropriate safety measures, you shouldn’t worry about ‘hacked’ attachments.
Q: What’s the effect of DMARC on emails with attachments?
To answer this question, we have to take a closer look at how emails with attachments get filtered. In the SMTP process (delivering your emails) the first obstacle your attachment encounters is the receiving mail server (MTA). This is where your emails get checked for DMARC as well. For this part, having a properly set up DMARC policy + a great sender reputation can increase your deliverability.
However, as we mentioned before, some recipients have extra spam filters. Not all will eliminate your attachments, but some have a taste of filtering out attachments they find spammy. In this case, DMARC is not going to help you: these spam filters do not check for email authentication. If this turns out to be a problem for you, you can either send a link to the PDF file or contact the spam filter about its malfunctioning.