Mail.app unable to login to 1&1 mail account after upgrading to macOS High Sierra I upgraded my iMac to macOS High Sierra 10.13.4. Since then my email account with 1&amp;1 (that was previously working fine) - decided to work intermittently, then just failed completely. I contacted 1&amp;1 and they couldn't help, saying I was using the right login credentials. They even screen shared and were still none the wiser and said it must be an internal problem.

I deleted the account from Mail.app and tried to Add Account - but it just says Unable to verify account or password. If I ignore that and just carry on filling in the appropriate fields, I get another window Select the Apps you want to use with this account. I check Mail and press next and there's spinning beachball connection icon for a split second and then nothing happens.

How do I get my mail account with 1&amp;1 to work again with Mail.app?
I had the same problem. The solution was in the Mail app itself to go to Preferences, select Accounts, and to enter the complete email myname@myisp.de as user name for my IMAP account.

I also had to change the port for IMAP to 993 and for SMTP to 465 (for secure connections via SSL.)