SMTP Error when adding account


I tried adding my institutions/schools account with imap/smtp. It is a hosted microsoft something, but not office365 and does not need exchange capability. With Thunderbird for example it works with imap/smtp.

The error message is

connect 587
421 4.3.2 Service not available

SASL_PATH: /usr/share/mailspring/resources/app.asar.unpacked

SMTP Last Response Code: 421
SMTP Last Response: 4.3.2 Service not available

mailsmtp Last Error Code: 1
mailsmtp Last Error Explanation: MAILSMTP_ERROR_UNEXPECTED_CODE
mailsmtp Last Error Location: 1
mailsmtp Last Auth Type: 0

The recommended setting specify port 25 or 587 with STARTTLS


It always happens with that account.

Email Provider

It is an institutional account, which probably means some exchange variety. Though for sure not O365.


  • OS and Version: Arch-Linux
    • Installation Method: aur / (uses the deb)
  • Mailspring Version: 1.13.3-9a7e1a78