[Mautic 5] Update documentation on Transactional emails now ignoring DNC setting

[RCheesley]

In Mautic 5 we are fundamentally changing the way in which transactional emails work. See https://github.com/mautic/mautic/pull/11786 for the background.

Current behaviour:

If a user has DNC set for the email channel, they will NOT receive any transactional emails. This is a problem as transactional emails relate to things which the user should be notified about even if they have opted out of emails - for example password reset, order updates etc.

New behaviour:

From Mautic 5, transactional emails will IGNORE the DNC setting and always be sent to the user.

This means we need to update the end-user documentation to make this abundantly clear.

⚠️ BE SURE TO MAKE THE UPDATE ON THE 5.x BRANCH OF THIS REPO SO THAT IT ONLY APPLIES TO THE 5.x VERSION! ⚠️

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[jos0405]

See https://github.com/mautic/user-documentation/pull/135 Campaign Action Email - description of Transactional and Marketing Email DNC behavior

[jos0405]

Here is the right PR to the M5 branch: https://github.com/mautic/user-documentation/pull/136

[mautibot]

This issue has been mentioned on Mautic Forums. There might be relevant details there:

https://forum.mautic.org/t/post-thanksgiving-boost-contribute-to-mautic-this-open-source-friday/30038/1