The practical limit on most cPanel/LiteSpeed mail servers is around 25–50 MB per message, including the attachment and any encoding overhead. Because attachments are encoded, a file uses roughly 1.4x its real size, so a 25 MB limit means files up to about 18–20 MB go through reliably.
Remember the receiving server also has its own limit, so even if your message sends, the other side may reject it. For large files, it is better to upload them to a cloud or file-sharing service and email the download link instead. If you need to send big attachments often and hit a hard limit in Webmail, please open a ticket and we can confirm the exact limit on your server.
