Hi we have a workaround that may work for some of you.
We use a “stamp” text in email body to identify a specific template in sequence. For example I put at the end of the template a unique referecence text like: Ref: seq-xyz and paint it and use a small text size so the recipient will not notice it. The stamp becames something like this:
Ref: seq-xyz
..at the last email line (if you prefer you can use a white text so it will became completely invisible)
To use it on a workflow you just need to have a condition that a engagement (activity) email sent contains in email body the stamp string (Ref: seq-xyz)
So the contact will be added to workflow everytime the email in sequence is sent with the stamp that matches the one you have used.
If you use this always take in count that in some cases your customer will clearly see the stamp ref text you’ve used for him (for example in cases that it uses a email client that converts html email to simple text).