El Capitan wrecked email.

For one mail account?

All mail accounts?

Try posing here since other updaters have had similar problems

OS X El Capitan

I have three email accounts. the iCloud email works. The other two only receive but do not send after upgrade. HELP

You should start your own thread, provide details, then your problem can be addressed.

I have a similar mail problem, cannot find a valid answer. We use two apple accounts and my partners account is working fine. Mine is a total disaster. All mail accounts gone, apple id, password rejected.

I wonder if the problem has to do with the two accounts on my iMac. On my laptop it's just me and everything is fine with 'El Capitan'

This is what I did to sort out El Capitan and Mail app issues, I had to wind back to Yosemite and start again with the install but it worked with this process:

Re: Mail not working with El Capitan