Hello Gilser and welcome to Apple Support Communities.
I see you have been having some kind of issue with Mail on a Mac running Mojave.
Are your email accounts all iCloud based (i.e., icloud.com, me.com or mac.com)? There was a reported outage in some iCloud services about the same time you posted this.
You can always check that status of various Apple systems here:
Apple - Support - System Status
If the issue is ongoing, some additional detail would help in terms of allowing the community to possibly chime in with answers.
Are you able to send but not receive? The opposite? Unable to either send or receive? If the accounts are not iCloud, then who is the provider? Is the app itself becoming unresponsive or crashing?
Cheers.