First off, I have to give you major props for such a detailed and specific question. I used the links you provided to better understand the problem-space as I never use that functionality myself and it was click, click, up to speed.
I was happy to take my time to test out a theory on your behalf since you were so respectful of my time. Thank you!
I tested out an approach that treats your +email address as an alias. Seems to address your needs. The only caveat is that you need to prepare any + addresses in advance, or on-demand. Solution adapts Gmail's existing Send As functionality (described at end).
+ Address as a Gmail Alias
- Navigate to the accounts tab in Gmail settings (https://mail.google.com/mail/u/0/#settings/accounts)
- Under 'Send mail as:' click 'Add another email address'
- In the email address field type in your +email address
- Leave 'Treat as an alias' checked, optionally customize the Name.
- Click 'Next Step'
- You are immediately returned to the settings page as the normal authorization phase to confirm ownership is redundant.
- Make sure 'Reply from the same address the message was sent to' is checked under 'When replying to a message:'
When replying it might appear that Gmail is reverting to your account email however do not despair, this is not the case and you can confirm that by running some tests using a second email account (Gmail or otherwise). Gmail is just showing off the fact that it recognizes the email address is essentially one and the same.
This next section is not necessary but was added to provide some additional information for users unfamiliar with the Gmail Send As
functionality which underpins this solution.
Gmail Send As Functionality
Gmail allows a user to send email from addresses they own but different from the account they are currently logged into.
Send emails from a different address
Send as addresses:
- can be from Gmail or other providers (e.g. Yahoo, Outlook, work, school, etc.).
- have the name and email address specified separately from your main Gmail address.
- can be set as aliases for the main account (alias option) which was indeed leveraged in this solution.
- can optionally have the reply address specified independently of alias address (not relevant in this solution).
The solution above leveraged the send as functionality with a twist by supplying the +address as the "separate" email address that message recipients would in turn reply to.
Note on Privacy: Using send as (or reply as) will not necessarily eliminate from the message ties to the original Gmail account from which it was sent. Although messages will be to and from the right email addresses , and it may not be obvious superficially in the recipient's email client, for various legitimate reasons information can be encoded in the message headers that exposes the actual Gmail you are using. This is particularly true when using them with the alias option checked, as is in this case. This note is general to send as / reply as since, in the case of +addressing, the address format itself obviously gives away your email address since it is everything that precedes the + in addition to @gmail.com :-).