Email is hosted through Uberspace. For new accounts, use Uberspace 7.
Add all desired email domains by running: uberspace mail domain add [domain.tld] (1)
The command will output the necessary DNS configuration.
Go into the Email section of the dashboard.
Start by adding the mailboxes under Your virtual mailboxes. Next, you can define aliases under Your additional mail addresses.
The mailboxes can optionally also directly be configured through the terminal (2) and the aliases are just .qmail files.
Disable the spam filter: uberspace mail spamfilter disable (3)
Emails from the old server can easily be migrated using imapsync. (4)
Create two files, oldpass and newpass containing the password of the old and new IMAP account, respectively. Then run:
imapsync --host1 [imap.oldhost.tld] --user1 [old_username] --passfile1 oldpass --ssl1 --host2 [host.uberspace.de] --user2 [new_username] --passfile2 newpass --ssl2
Afterwards, delete those files.
see 5