Splitting email lists naively on commas is unreliable [#3579633]

Problem/Motivation

If an to email is entered for example as `"Paris, Thomas"` the address won't be added correctly and in some cases will fail sending entirely because of splitting on the comma in the name.

Steps to reproduce

Send an email to an address with a comma in the name.

Proposed resolution

Use a library that supports RFC2822 - like mmucklo/email-parse.

Remaining tasks

Tests...

User interface changes

none

API changes

none

Data model changes

none

Issue fork smtp-3579633

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3579633-splitting-email-lists changes, plain diff MR !73
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