Fixes IMAP UTF8 Authenication

[stumpylog]

Proposed change

In the event of a UnicodeEncodeError during normal login, we'll now try to fallback to an AUTH=PLAIN login type, which encodes the username and password differently.

I successfully tested this with a password containing UTF8 characters and was able to view the inbox.

Fixes #663

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other (please explain)

Checklist:

• I have read & agree with the contributing guidelines.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• If applicable, I have checked that all tests pass, see documentation.
• I have run all pre-commit hooks, see documentation.
• I have made corresponding changes to the documentation as needed.
• I have checked my modifications for any breaking changes.

[stumpylog]

If we can sneak this into the beta, it's probably good to.

[shamoon]

Thanks as always for another deep-dive fix! In the case of the new plain auth attempt is the error output still clear? Im just wondering if it would be helpful to include something like "non-ascii chars detected, attempting to fallback to plain auth" to make it more apparent why this all failed?

[stumpylog]

Well, the error before was pretty generic, so I kept that, but I could see having an extra log or two would help in debugging

[coveralls]

Pull Request Test Coverage Report for Build 2222357777

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 91.985%

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Files with Coverage Reduction	New Missed Lines	%
paperless_mail/mail.py	6	96.86%

Totals
Change from base Build 2222108065:	0.04%
Covered Lines:	4315
Relevant Lines:	4691

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💛 - Coveralls

[qcasey]

This looks ok to me.

[stumpylog]

This is a pretty minor change to me, do we want the pending reviewer still or just merge?

[qcasey]

Agreed, let's just merge. This happens a lot, we might have to revisit that rule later on

[github-actions]

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