All e-mail service providers limit the maximum e-mail size that an account can send and receive. Each provider has their own size limit.
The size limit applies to the combined size of all the elements of the message, including text, headers, and all attached files.
If you have a free e-mail account and try to attach files bigger than 50 MB, you may receive a notification informing you that the attachment size has been exceeded.
Basically, a free account gets a low maximum e-mail size limit, but you can increase the maximum size limit by upgrading to a paid account.
As a mail.com Premium subscriber, you can send and receive e-mail messages and attachments up to 100 MB in total size.