On 2021-02-08 16:14, Bill Cole via mailop wrote:
On 8 Feb 2021, at 17:03, Richard Bewley via mailop wrote:
The critical feature in '+' tagging (and equivalents using other characters or patterns) is the ability to create aliases on-the-fly in a namespace that the user controls such that the mail system handling delivery only needs to know the tagging pattern rather than every new tag.
In a previous life I had an email system that would sort tagged messages into a subfolder, but only for folders that existed. If a folder didn't exist the message would get rejected at SMTP time.
Not many users used it or grasped the concept of giving out a different address to each company, but the idea you could actually revoke a sender's ability to send to you just by deleting a folder was well received.
Since some companies didn't accept tags, we allowed a - instead, and t...@mailbox.example.com would get aliased to mailbox+...@example.com. But of course now users have even more possible addresses they might have given out, which increases confusion significantly for those who didn't really get how tagged addresses worked but tried anyway.
The "de-tagging" tactic that Al noted has existed, although I don't see much evidence of it in recent years. I think it may be that enough people who use tagged addresses give tagged addresses less scrutiny that senders who paid attention noticed that de-tagging hurts deliverability.
There is also the possibility to give anything missing a tag extreme scrutiny (or outright reject it) if a user is careful to never give out untagged addresses.
By definition there is no consent given to a sender who just makes up their own addresses (by stripping or changing tags), which is significant to any sender trying to operate on an opt-in basis.
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