Dovecot Help (fixed from earlier)

[david]

Folks

I recently switched from Centos/Sendmail to Ubuntu 
20.04.2/Postfix/Dovecot.  Most of the functions I need are working 
except reading mail from an iPhone.  The mail server is on my own 
machine, and the mail client is on my iPhone.  I use Secure POP.
The symptom I think I see on the server is an authentication failure, 
but I'm sure my passwords are correct (I do control both the iPhone 
and the server).  What information would help diagnose and hopefully 
fix the problem?
Thanks for your assistance.

David

I asked earlier and omitted the reference to Dovecot.  My error.