A Brief Guide to Email Attachments - Deliverbility

A Brief Guide to Email Attachments

Email attachments are one of the guaranteed ways to attract your recipient’s attention.

Now, what are email attachments? In retrospect, they are files added to the email message body bringing some extra value to it. These may be files of various formats, sizes, and contents.

As you know, adding an attachment is a pretty straightforward process, but there are certain limitations, especially when it comes to email campaigns. This is why we’ve created this short guide to elucidate the do’s and don’ts of email attachments.


  • The element of trust
  • domain or IP reputation
  • Different Attachment formats
  • Attachment size limits
  • What is Deliverability
  • HTML
  • Additional relevant tips

The element of trust: An email attachment may seem suspicious

Attachments are often utilized by marketers when writing a professional email copy as a way to give more value to the message being delivered and incentivize the user to open it. If you are reaching out to specific prospects and use attachments as a way of personalization method, it might work wonderfully.

But when we are dealing with cold emails, including anything else besides the actual text can seem shady.  This may be obvious, but many marketers forget that when a recipient receives the message with an attachment from an unknown source, they are likely to believe it’s malware.

Cold emails aren’t a bad thing per se, but attaching a file to it makes it appear far more suspicious and makes it more complicated for emails to avoid the spam filters. This can put your emails in the spam folder, labeled by the mail client or ISP, inevitably hurting your sender reputation and harming your prospective email campaigns.

Additionally, many people ask, “Should you explain your attachments in business emails?” The answer is a straightforward and resounding “yes,” of course. Explaining the attachment makes it sound a bit more trustworthy. That is why you should try not to send any email message that contains only the attachment – it doesn’t look professional at all and doesn’t raise any trust.

Domain or IP reputation: attachments have a very negative impact

Once again, utilizing attachments in cold emails can throw a wrench in your campaigns. Bulk cold emailing with the help of attachments is likely to result in a high number of subscriber complaints. Each and every domain on the web is identified by the ISP before its processed further, allowing to block any pirate content or adult web pages through the labeling of IPs and domains. A high complaint rate can catch your ISP attention.

In our case, the email address or IP you use for cold emailing can be flagged by your ISP, and your email message will either end up in the spam folder or get blocked entirely.

Hence, email attachments in cold emails can lead to the utter deletion of your email domain from a list of reputable sources. Use these only in a small personalized email campaign or with your existing clients.

Attachment formats: a wrong attachment format can lead to email block

So you’ve decided to use attachments for your campaign email. It will help if you ensure that people will feel confident enough to open it. First of all, your email message must convince the receivers to open and download the email attachments. If it’s not a problem, be mindful of this one significant rule.

Never send anything with documents or images. In most of the cases, the user will never download any other attachment besides a clearly visible image or document. It’s best to keep your attachments in .pdf .txt, .jpg, and.gif, formats.

PDFs can be a great addition to any nurturing email, but they can be challenging to create and edit. You can find how to edit a PDF file easily from our friends at JotForm.

If you still want to send a file in a different format, ensure that you are using an acceptable attachment format because every ESP has its own limits on file formats (for instance, look through at Gmail attachment limits here).

Size limits: follow email attachment limits for excellent deliverability

Want expert advice on the size of email attachments? Various Email servers and clients have email limits, so make sure you follow them strictly. Moreover, email clients may reject your emails as a whole because of their size. Try to keep your email body within 15-100kb limit, with files no more larger than 10mb.

If you still need to send a bigger file, it’s generally more acceptable to attach a link to the file on Google Drive. Besides hosting large files, Google Drive will check the file for any malware, solving the trust issues.

The email attachment size limits discussed above are considered universal in case you don’t want to get caught in spam filters.

Deliverability: attachments can stop your email from reaching the inbox

Reducing the attachment size of your emails is one way to increase the deliverability of your messages.

Having an attachment won’t automatically destroy your deliverability. Email clients won’t filter you for having images between 20kbs and 50kb in size. Nevertheless, if you decide to insert a half MB image, you are not safe from being labeled red by the email clients.

This happens because many email spammers love to use images to mask the text of their messages, undetectable to email filters. To keep your deliverability high, you should stick to under 60kb image attachment size limits. This research by EmailOnAcid goes into furtherdetail on the effect of the file size on deliverability.

HTML attachments: files may not be displayed in the right way

An attachment is not just merely a file: it can be an HTML styled template with some text in it. Many companies tend to use these for promotional content instead of plain-text emails.

With styled HTML attachments, you can create content that’s far more appealing to the audience than plain text. The problem is these templates usually don’t load well on every email client and device. In fact, not all templates are even correctly optimized for a mobile view.

While utilizing HTML templates can help you use colors in a creative way in email marketing to improve your conversions, they should be used very carefully. Keep those two points in your mind when deciding or creating a template.

Additional tips

How to add attachments to an email? Here are the best tips for you to follow:

Use all attachments as additional information to plain text email. Take advantage of the cold email formulas to readily convert leads.

If you use email templates, ensure that they don’t overload your email size-wise. You should also check the email sending limit of your ESP to know your email limits.

Unless the file you’re sending is profoundly personalized (a custom report, a ticket, a personal invitation, a document, etc.), you have significantly higher chances using a link to the file instead of the attachments emails.

Save email attachments for campaigns to your existing customers and warm leads.


While email attachments are quite a usual sight for marketing, there are particular rules you have to follow to retain your email deliverability high. If you’ve already taken proper care of your sender reputation and use an email checker to clean your list before sending, the main feature you still have to pay attention to is the attachment size limits – the smaller the file, the greater your chances to get into the recipient’s mail inbox.

Try to avoid sending any files to cold leads: your emails can be deleted or reported as spam if there’s no established relationship between you and the recipient.