What is the maximum size of an e-mail message?

You can define the maximum size of an e-mail under Incoming - Protection settings > Limitation of e-mail size. By default, a maximum size of 50MB is set. The value can be extended to a maximum of 2048MB.

If you don't want to use any limit, then you can check the option No limit.

Furthermore, you can specify what action should be taken by EuropeanMX when a message of this size is received. By default, such a message is rejected and the sender receives a corresponding notification from the system.