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Your LimeSurvey version: [see right hand bottom of your LimeSurvey admin screen]:  Version 4.1.16+200407

My organisation introduced  two-factor authentication for our mails (Outlook) and now we are no longer able to send out surveys to participants via lime survey. We receive an error message when trying to send the surveys: SMTP ERROR: Password command failed: 535 5.7.139 Authentication unsuccessful, the request did not meet the criteria to be authenticated successfully. We already double-checked the mail address and password. They are correct.  Does anyone have similar problems or know whether we need to do changes in the settings of lime survey?
 

I am not sure if a web app like Limesurvey can cope with two-factor authentication for email, maybe someone with more knowledge about this can provide some more insights.

But another thing:

Version 4.1.16+200407

This version is now over 2,5 years old, and thus hasn't received any bug fixes or security updates for 31 months.

In addition to this, LS 4.x was soon changed to LS 5. I personally would not consider any of the LS 4.x releases as stable enough for production use. I would highly recommend to update to the latest LS 5.x release.

In my opinion, this old thing shouldn't be accessible from the internet anymore. I have no idea if GDPR is relevant for Switzerland, but you probably have something similar then. If there is a data breach, it will be difficult to argue that everything was done to protect data by using state of the art software, when this software hasn't received any of the available updates over 2,5 years.

Kornfeind1 wrote:

My organisation introduced  two-factor authentication for our mails (Outlook) and now we are no longer able to send out surveys to participants via lime survey.
 

You need to get in touch with the IT department of your university. The mailing list of your university indicates a confusion about what was changed.
lists.zhaw.ch/mailman3/hyperkitty/list/l...RHY377NF2ZF3ONSYIO7/

Microsoft and others switch from Basic authentication to OAuth2 (which is not 2FA!).  Microsoft still allows sending mails via SMTP without OAuth2,
LimeSurvey hasn't implemented support for OAuth2. Using IMAP or POP3 isn't possible with Microsoft365, but SMTP is possible.

But your university might have deactivated or restricted SMTP. If that is the case, you will not be able to use LimeSurvey with an email account of your university Microsoft365 infrastructure.