Description

When a new version of docker-mailserver is available the account used in this tests also gets the postmaster notification for the new version. The mailbox then may contain 2 mails but only one with 'This is a test mail.'.

Fixes #3251

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes