Sometimes the default email message size with cPanel / WHM is not large enough and requires adjusting. Configuring this to a specific maximum size can be done as follows:
Log into WHM.

Under ' Service Configuration' , select ' Exim Configuration Manager' and go into the ‘Advanced Editor’.
.png?sv=2026-02-06&spr=https&st=2026-07-30T10%3A07%3A48Z&se=2026-07-30T10%3A18%3A48Z&sr=c&sp=r&sig=3VCMnkPiIpUJbs%2FaZ%2Bd%2FY4SiPCQrHWhO8%2BE1VUfHwmg%3D)
Search for a large blue 'Add additional configuration setting ' button and click to select from a drop down list.
.png?sv=2026-02-06&spr=https&st=2026-07-30T10%3A07%3A48Z&se=2026-07-30T10%3A18%3A48Z&sr=c&sp=r&sig=3VCMnkPiIpUJbs%2FaZ%2Bd%2FY4SiPCQrHWhO8%2BE1VUfHwmg%3D)
Select 'message_size_limit'.
.png?sv=2026-02-06&spr=https&st=2026-07-30T10%3A07%3A48Z&se=2026-07-30T10%3A18%3A48Z&sr=c&sp=r&sig=3VCMnkPiIpUJbs%2FaZ%2Bd%2FY4SiPCQrHWhO8%2BE1VUfHwmg%3D)
Enter the desired limit for a message size (the default is 50 MB).
.png?sv=2026-02-06&spr=https&st=2026-07-30T10%3A07%3A48Z&se=2026-07-30T10%3A18%3A48Z&sr=c&sp=r&sig=3VCMnkPiIpUJbs%2FaZ%2Bd%2FY4SiPCQrHWhO8%2BE1VUfHwmg%3D)
To finish and save your changes, select 'Save'.
.png?sv=2026-02-06&spr=https&st=2026-07-30T10%3A07%3A48Z&se=2026-07-30T10%3A18%3A48Z&sr=c&sp=r&sig=3VCMnkPiIpUJbs%2FaZ%2Bd%2FY4SiPCQrHWhO8%2BE1VUfHwmg%3D)
Note: If you do not also increase the maximum allowed attachment size in Webmail, you will still be unable to attach files larger than 50 MB in Webmail.