How to auto detect a remote IMAP/POP3 server given only an email address ?

I want to be able to allow people to check their email from my PHP
online application.

Given only the users 1) email address, 2) username (if applicable) and
3) password - how can I auto detect a remote IMAP/POP3 server so that
I can connect and fetch mail for the user. (Ultimately, I don't want
users to have to know what the IMAP/POP3 server name / port is .... I
would like to auto-detect all of that).

At first I thought I could use "getmxrr" but quickly realized that is
only good for determining the SMTP server.

If anyone has ever "add account" in Gmail Preferences, it's
essentially the exact same functionality where Gmail auto-detects the
IMAP/POP3 server.

Any help will be greatly appreciated.

.

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