We forward email with attachments for up to 50Mb per email(including messages and attached files) . The size limit applies to the combined size of all the message elements, including text, headers, and all attached files. A server can only process so many requests at the same time, these size limits are put in place to avoid a total system collapse. Attaching files larger than 50 MB will result in a bounce-back email notification informing you that the attachment size has been exceeded.
Email size limits are used for performance, database size and security reasons:
Performance. Email systems are not designed to transfer large volumes of data.
Database/storage size. Email data have limits because they are stored on a server.
Security. A large number of messages could take a whole system down. Email systems usually use a limited number of ports to retrieve data. This makes them candidates for potential security vulnerabilities( DoS attacks)
An email service provider dictates its limit by performance and security reasons. When preparing your email newsletters, there are things you should keep in mind from the maximum size of file attachments and the HTML part to the email client of the recipient to email deliverability.