Hello y,
I hit the same issue couple of days ago. At some point during my vacation email login started failing. Checked what's in the Lansweeper config, looked good. Checked if mail account is locked, wasn't. Restarted the Lansweeper service, no success. Resetted the password for mail account in the mail system (Exchange), went back to Lansweeper and still fails. Next I logged to mailbox and read some mails, so account and password must be good. Opened once again Lansweeper config and typed in the same password again and closed config. Suddendly it works. Don't know why, but mails flow.