URLs in emails generated by C# application are transformed on arrival

Question

One of my users has raised a request to look into an issue they are coming into, and I am stumped.

They have written a piece of code in C# to send an email out, using these settings:

"port": 25,
"deliveryMethod": "Network",
"useDefaultCredentials": true,
"host": "localhost"

Within the email, there is a URL link to a page on confluence, which is perfectly normal, and when the program is run from his local machine, this works properly, however, when sending through one of our servers (Windows Server 2012, R2) , the URL gets transformed, into something like below:

http://url9145.codehousegroup.com/wf/click?upn=WP2ufi4-2Bse9p6RLS7OZb1m6403-2BGEy2DR-2FGCBzoKSvTLc3cMTOPz2-2F9rL3fb-2BPZWE9pMxBm1BbD86haPjxxUwX1rQMcG6hI-2BwwJPqFrTnUK2zGfFMRfPdkDljJ-2BFeTfvLhEqJM-2BNtCyNVokPD6pDbfhqdICcRMfBfB0D7SazWcc-3D_yEp1Kj7ZSu-2FRHJ2NseEckLf6DkJfeCKXG8psbI3UQXpz-2B120qcGRyGogIShHC4ELnrkhHVrbaAJ0jm-2BzUY5kIX-2hkSK2q3dKnBU0UmS-2FO5tqG2iAXBO3lfSkGWkH4osAvZm-2BRIv0gQT7j88tu9I7isTWdSjwqinW0PyTNVcB9toLY7jlY0MbN-2FZHHjfbyIcmbfxK1H-2FitshAY4coPBrPEoH53GNeSerhUqtA3DhA2NAFo-3D

(link changed slightly)

The original URL was

https://codehouse.atlassian.net/wiki/spaces/APM/pages/1354236014/2019-04-15+Azure+Elevated+Access+Prolongation

I for the life of me cannot fathom why, any ideas?

Answer 1

The /wf/click?upn= is a bit of a giveaway - these are tracking URLs that the mail server is putting in place of the originals.

Tracking URLs can be used to protect against malicious websites on click rather than filtering / scanning every URL in each email.

They are often used to track who clicks on what parts of an email, and can be quite useful for marketing campaigns and other studies.

They can also be concerning to the cautions and partially-informed user.

You could talk to your IT department and try adjusting or disabling this feature... or send via another mail server without this "feature".

---

Does your company happen to use SendGrid by any chance?

Enabling Click Tracking causes all the links and URLs in your emails to be overwritten and pointed to either SendGrid’s servers or the domain you branded your link with so that any time a customer clicks a link, SendGrid can track those clicks. _Source

There is mention of this URL format specifically on their "Universal Links" page:

https://links.example.com/wf/click?upn=