HTML signatures with mu4e and Gmail
For a long time I've been searching for an email client that would fit my workflow. During my macOS days I was a happy Airmail customer, though I can't say that it adapted to my workflow more than I adapted to it. Then they decided to change to the subscription model and charge for "premium" features such as push notifications, and that's when I decided to stop using it.
Now I'm back in GNU/Linux and I've tried several clients: Thunderbird, Geary, Claws, KMail, etc. None would meet the demands I had on a suitable email client. After much consideration I decided to take the plunge and use mu4e as I already use emacs for many other of my computing needs.
I'm not going to describe how my mu4e workflow works as I'm still working on it. However one particular issue I found while setting up everything caught my attention on the basis of not being something that you necessarily think it will be complicated to set up, but it ends up being complicated for different reasons.
Email signatures
While it used to be very common to have an email signature, nowadays it's more common in the workplace. Sometimes your employer will require a particular signature, usually with some HTML, images, etc. So even if you wanted to stick to plain text emails, unfortunately it's not your decision to make.
Attempt 1: HTML signature in mu4e
mu4e as any email client has support for signatures. The variable
mu4e-compose-signature can be set to any text you want.
For plain text emails this is very easy, set mu4e-compose-signature
to the text you want, and be done with it. For HTML emails it's
actually more complicated. If you add the HTML code directly to this
variable, when mu4e processes your email it will add the signature
content to the HTML body, and the recipients will view the HTML code
instead of the intended signature.
In my config I have a hook (add-hook 'message-send-hook
'org-mime-htmlize). I have this set because practically all messages
I compose are sent as HTML (unfortunate, but that's the reality we
live in). org-mime-htmlize doesn't know about your HTML signature so
it takes your whole message, including its signature, treats it as
plain text, and converts it to HTML.
What we need is some way to tell org-mime-htmlize to ignore our
signature while doing its thing. Adding a colon : character in front
of each line of your signature will do just that, as it tells
org-mime to format the preceding text as preformatted text.
This works relatively well, but…
Attempt 2: Base64 embedded image
In enterprise / work email setups, it's rather common to have an image as signature. I find this annoying but I can't change this practice. In my case the image is hosted in a publicly accessible URL so it should be a case of just using the right URL in the HTML signature right? Wrong.
My work email is hosted by Gmail. When my signature is sent, Gmail blocks the signature image from loading. I figured that encoding the signature as Base64 and using Data URLs would take care of the problem, but Gmail refuses to load it, I guess out of security concerns.
Attempt 3: But it works in Gmail
What I ended up doing is rather simple. First I sent an email to myself using the Gmail interface. The message arrived and the signature displayed correctly. I inspected the source of the signature and sure enough, it contained a different URL for the image:
<img alt=\"LoanPro\" src=\"https://ci5.googleusercontent.com/proxy/bl9k6Zg3juNxy-Cz5ETAa185cjwwciBBhzjk9ltCtHvEuF7mpsnQ7DTHpPL-pSfwofvuQyzoSxeiyCSEp3qQH6GKlnanrbiWrMvhackSiwdsmA_h2ywYVXw=s0-d-e1-ft#https://loanpro.io/wp-content/uploads/2020/07/cropped-new-logo-2-1.png\" style=\"max-width:120px;margin-top:8px\" class=\"CToWUd\">
Note how the original source of the image, hosted in the loanpro.io
domain, is included in the rewritten URL. So I simply copied this
rewritten URL, included it as signature as described in Attempt 1, and
that was it!