Vikunja installed on YunoHost testmail fails

sending a testmail fails with error:

553 5.7.1 <vikunja@m.mydomain.tld>: Sender address rejected: not owned by user vikunja

when i try to create a yunohost account “vikunja” under the domain m.mydomain.tld i got an error:

The login name already exists in the list of system accounts

thanks in advance

How did you configure the mailer in Vikunja? Can you share your config?

This looks like an error with your system though, not sure if I can help you there.

this is the mailer config

  enabled: true
  host: "localhost"
  port: 25
  authtype: "login"
  username: "vikunja"
  password: "12d5df14b6d14add5e5e422a"
  skiptlsverify: true
  fromemail: "vikunja@mail.mydomain.tld"
  queuelength: 100
  queuetimeout: 30
  forcessl: false

Iam creating a new user in yunohost and change the /opt/vikunja/config.yml mailer: entries to this user and now it works fine.