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Addresses some of the unlisted sender issues in 3.2.2. Allows clients to use mail white/blacklist, mail catchall's allowed to send as any domain address, client template limits for white/blacklist.

See https://www.howtoforge.com/community/threads/sender-address-rejected-user-unknown-in-virtual-mailbox-table-from-webmaster.85946/

Also closes #6018 (closed)