A Short Guide To Email Attachments The Do’s, The Don’ts, And The Why’s


    Email attachments is one of the certain ways to attract your recipient’s attention.

    Creating an attachment is pretty straightforward, but there are limitations, especially when it comes to email campaigns. Which is why we’ve created this short guide to explain what exactly can go wrong and how to avoid it.

    The Element Of Trust

    Attachments are often used by marketers as a way to give more value to the message and incentivize the user to open an mail. If you are trying to reach out a specific prospect and use attachment as a sort of personalization method, it might work.

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


    Cold email isn’t a bad thing per se, but attaching a file to it makes it look far more suspicious. This can put your email in the spam folder or worse, labeled by the ISP or mail client, inevitably hurting your sender’s reputation and harming your future email campaigns.

    IP or Domain Reputation

    Once again, using attachments in cold emails can throw a wrench in your campaign. Bulk cold emailing using attachments is likely to result in a high number of complaints. Every domain on the web is identified by ISP before it’s processed, allowing to block pirate content or adult web pages through labeling of domains and IPs. High complaint rate can catch your ISP’s attention.

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


    Therefore, email attachments in cold emails can lead to the filtering of your email domain name from a list of reputable sources. Use them only in small personalized email campaigns or with your existing clients.

    Attachment Formats

    So you’ve decided to use an attachment for your campaign email. You need to make sure people will feel confident and interested enough to open it. First of all, your email message in itself must convince the receiver to open/download the attachment. If that’s not a problem, be mindful of this one rule.

    Never send anything besides documents or images. In most cases the user will never download anything besides a clearly visible document or image. It’s best to keep your attachments in .txt, .jpg, .gif, and.pdf formats. PDFs make a great addition to any nurturing email, but they can be difficult to create and edit. You can find out how to edit a PDF easily from our friends at JotForm.

    Size Limits

    Email servers and email clients often limit the size of the attachment. Moreover, email clients may reject your email as a whole because of its size. Try to keep your email message body within 15-100kb, with files no bigger than 10mb.

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

    The file sizes described above are considered universal if you don’t want to get caught in a spam filter.


    Reducing the size of your email is one way to increase the deliverability of your message.

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

    This happens because email spammers love to use images to hide the text of their messages, undetectable to filters. To keep your deliverability high, stick to under 60kb image size.This research by EmailOnAcid goes into more details on the effect of the file size on deliverability.


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

    With styled HTML attachments you can create content that’s far more appealing than plain text. The problem is these templates often don’t load well on every device and email client. Not all templates are optimized for mobile view. Keep that in mind when choosing a template.

    Additional Tips

    • If you use email templates, make sure they don’t overload you email size-wise.
    • Unless the file you’re trying to send is highly personalized (a ticket, a personal invitation, a document, a custom report etc.), you have higher chances using a link to the attachment.
    • Save email attachments for campaigns to existing customers and warm leads.
    • If you want to find alternative ways to grab your lead’s attention check out these 8 methods.


    While email attachments are a usual sight for marketing emails, there are certain rules you have to follow to keep your email deliverability high. If you’ve already taken care of your sender reputation and always use an email checker to clean your lists before sending, the main characteristic you still have to pay attention to is the size of the attachment – the smaller the file, the higher your chances to get into the recipient’s inbox. Try to avoid sending files to cold leads: your email can be deleted or reported if there’s no established relationship between you and the recipient.

    Yaroslav Panyok is an author and researcher for Snovio Labs, providing readers with unique insights into marketing. Passionate about data, email marketing, and pizza, Yaroslav creates articles of any scale and complexity to compile research into something worth dedicating your time to. He is also a proud owner of a red fluffy furball named Ginger.


    Leave a Reply

    More in Marketing