Quoting Jochen Bern <Jochen.Bern@binect.de>:

On 27.06.22 00:52, Steve Dondley wrote:

I have a small client whose insurance company insists they have MFA for their email to be covered under some kind of data protection policy. Currently I have the client set up on a Debian box for the email server coupled with roundcube for webmail. Most the users just use roundcube but some also use their mobile devices to check email. Maybe one person uses outlook. There’s about 5 to 10 users total.

I know roundcube offers a MFA plugin. But I don’t have the foggiest idea how of an iPhone, Android device, or Outlook could all be set up to work with MFA with a standard dovecot/postfix setup. Are there any practical solutions for easily implementing MFA that could work across multiple devices?

*Totally* theorizing here, but as far as I'm aware, the SMTP (AUTH), POP, and IMAP protocol definitions do not provide elbow room to make *two* rounds of authentication. (Ever pondered why the admin can require O365 users to "use 2FA", but users then are still allowed to create "application passwords", note plural and lack of standard password features like a limited lifetime for those?)

I implemented PrivacyIdea as a backend auth mechanism for dovecot once in the past.

I honestly don't recall the details, and I wasn't sure how to do it dynamically with multiple domans, but one domain worked fine.  It was due to the PI 'realm' separator being @, and using full email addresses for the username. 
I believed I used OTP for the user's webmail password and 'device password' for imap/smtp.

Rick