Reply To: Problems with HTML email signatures not appearing in replies

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I don’t see a solution as it is out of your client’s control what another person’s email does, or doesn’t do.

Absolutely.

And it’s not something that should be in your control. Keep in mind that many email clients (either by default, or through user preference) disallow inline HTML images, and rightfully so: it’s a privacy and security issue. <img> tags in emails are used for tracking/marketing, finding vulnerable targets, and as an attack vector.

The best approach is to duplicate the info in the image in a plain text version of the signature and send both. (You should be taking this same approach with the email itself, as well: if you’re sending an HTML version, always include an alternative part in plain text.)