How does email file size and MIME types affect email deliverability?

Email marketer from Email Geeks shares that deliverability is considerably reduced when an AMP part is sent to Outlook. To mitigate this, they only send the HTML part to users with an @outlook or @hotmail address.

Email marketer from StackOverflow user MailGuru explains that using correct MIME types ensures that email clients properly render the email content. Incorrect MIME types can cause emails to display incorrectly or be flagged as spam.

Email marketer from Reddit user EmailPro mentions in a thread that large emails often have problems with mobile display and slow loading times, leading to poor engagement. He advises keeping emails lean and mobile-friendly.

Email marketer from Email on Acid explains that keeping emails below 100KB improves deliverability and ensures the entire email is visible. Clipping can lead to missed calls-to-action and tracking pixel issues.

Email marketer from Gmass shares the importance of testing your emails before sending them out to large contact lists. They highlight the use of Google App Script, with it you can preview the total size of your email

Email marketer from Mailjet explains that the size of your email can impact deliverability. Larger emails can take longer to load and may be flagged as spam. Optimizing images and compressing content can help reduce file size.

Email marketer from HubSpot shares that large image sizes and unoptimized HTML code can trigger spam filters. Keeping emails lightweight and optimized helps ensure deliverability.

Email marketer from Sendinblue shares that email design best practices include keeping the HTML email file size under 100KB to avoid clipping in Gmail and other email clients. This ensures that the entire message is displayed, including tracking pixels and calls-to-action.

Email marketer from Litmus shares that oversized emails may trigger spam filters. He recommends optimizing email size by compressing images, minifying code, and avoiding unnecessary attachments.

Expert from Email Geeks explains that when mail is clipped, the bottom isn’t rendered, which often contains the open tracking pixel, leading to misinterpretation as a delivery issue.

Expert from Email Geeks shares a case where overly simplistic CSS media queries blew up a pixel from 1x1 to 300x300. He explains ESPs add tracking pixels at the end of emails to avoid issues and reduce customer service calls.

Expert from Email Geeks explains that a tracking pixel can break rendering, and this is more obvious when placed at the top, particularly if the pixel doesn’t load or is blocked, resulting in a broken image at the top of the email.

Expert from Email Geeks explains that injecting tracking pixels at the top of the HTML DOM carries a bigger risk of breaking rendering for the whole email because it is usually injected in a crude manner. He suggests using a templating setup where the ESP provides a function to place the tracking pixel safely.

Expert from Email Geeks explains emails longer than 100kb are often clipped in Gmail, which is not a deliverability issue but affects customer experience. Size is "on the wire," including headers. She also mentions that aboutmy.email will show the size of your email. While she has not seen recent data contradicting the Email on Acid's findings, she expects that filters have improved since 2014 and are not solely looking at size.

Expert from Spam Resource explains that larger email sizes can negatively impact deliverability. ISPs and email clients may be more likely to flag larger emails as spam. Optimizing images and using efficient HTML code can help reduce file size.

Expert from Word to the Wise answers question about ensuring that emails use the proper MIME types for the content they contain. Incorrect MIME types can cause display issues or trigger spam filters, negatively impacting deliverability. It is important to check the proper formatting of these.

Documentation from Google Workspace Admin Help specifies that Gmail has a message size limit of 25 MB. This includes all attachments and inline images. Exceeding this limit may result in the email being rejected or undelivered.

Documentation from Microsoft states that Exchange Online has a maximum message size limit of 150 MB. Emails exceeding this limit will be rejected. Understanding and adhering to these limits is crucial for ensuring email deliverability within the Exchange Online environment.

Documentation from RFC Editor outlines standards for Internet Message Format, including the structure of MIME types. Correct MIME type declarations are essential for proper email rendering and avoiding spam filters. Misconfigured MIME types can lead to emails being interpreted incorrectly or flagged as malicious.

Documentation from IETF explains that Multipurpose Internet Mail Extensions (MIME) specifies how to include various types of content in email messages, such as text, images, and attachments. Proper MIME encoding is crucial for ensuring that emails are correctly interpreted by email clients.