What are the attachment and message size limits for different mailbox providers?
Summary
What email marketers say8Marketer opinions
Email marketer from Constant Contact recommends keeping email attachments below 5 MB for optimal deliverability and user experience.
Email marketer from Reddit user u/EmailPro explains that many corporate email systems have a strict 10MB limit due to security concerns, and exceeding this will bounce the email.
Email marketer from Sendinblue explains that it is best practice to keep attachments under 2 MB to ensure deliverability. Suggesting the use of cloud storage services for larger files.
Email marketer from Reddit user u/TechGuru suggests using cloud services like Dropbox or Google Drive to share large files instead of attaching them directly to emails.
Email marketer from Email Marketing Forum user MailMaster states most ISPs recommend keeping your total message size (including attachments) under 15MB to avoid delivery issues.
Email marketer from HubSpot highlights that large attachments are one of the factors that can trigger spam filters, and suggests optimizing images and using links to documents instead.
Email marketer from Litmus advises that large attachments can negatively impact email deliverability and recommends using cloud storage and linking files instead.
Email marketer from Mailjet shares that the acceptable attachment file size varies depending on the email client used. Many clients limit attachments to 10 MB, but some may allow up to 25 MB.
What the experts say5Expert opinions
Expert from Email Geeks shares that they haven’t seen a message size limit lower than 10 megabytes recently.
Expert from Email Geeks explains that if an attachment is base64 encoded, you can multiply the attachment size by 1.34 to estimate the byte cost on the wire.
Expert from Word to the Wise explains that attachments are often base64 encoded, increasing their size by roughly 33%. So, for a 10MB attachment, you need to account for about 13.3MB on the wire.
Expert from Email Geeks shares that the `SIZE` response to `EHLO` tells you how many encoded bytes a server will accept in the body of an email.
Expert from Email Geeks explains that the limit is on the maximum size of the message on the wire, not specifically an attachment limit.
What the documentation says6Technical articles
Documentation from Microsoft Support explains that Outlook.com has an attachment size limit of 20 MB. For Microsoft Exchange accounts, the default limit is 10 MB but can be configured by the administrator up to 150MB.
Documentation from Google Support explains that Gmail has a message size limit of 25 MB. If you need to send larger files, use Google Drive.
Documentation from Zoho says that the maximum attachment size is 20MB for standard plans and 25MB for paid plans. Recommending using Zoho Docs to upload larger attachments.
Documentation from IONOS states that the size limit is dependent on the email package you have. Suggesting you check the details of your package for the specific limit.
Documentation from GMX explains that the total email size limit is 50 MB but that this includes encoding overhead, therefore the attachment should be smaller
Documentation from Yahoo Help explains that Yahoo Mail has a message size limit of 25 MB.