mailman: Enable VERP

Improve bounce detection.

Also reduce the number of recipients per single SMTP delivery.

added 4 commits

• 7f2f7e50...bdae25a5 - 3 commits from branch master
• 05d5617c - Enable VERP for (some) outbound emails

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added 1 commit

• abdbddde - Fix CI build

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added 1 commit

• 21c06a78 - Small fix

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mentioned in commit 99e52be5

merged