Update mail.md to detail Thunderbird setup w/o Exchange (#134)

* Update mail.md to detail Thunderbird setup w/o Exchange

Lets you not pay 10$ a month for basic utilities, at the cost of needing to re-log once a month instead

* Update mail.md

Updated instructions to be more generalized, and that they are volatile until further testing can be done

Please let me know if anything else needs adding, or if you have tested with other (non-Thunderbird) clients. Thank you!

onboarding/computer-setup/mail.md

@@ -30,4 +30,14 @@ Incoming Mail Server: zimbra.polymtl.ca
 Outgoing Mail Server: smtp.polymtl.ca
 ```
 
-Click `Sign In`
+## Add PolyMTL email to Email Clients without Exchange
+
+This solution uses OAuth2 instead of Exchange, avoiding the need for your client to have root level permission on your operating system. However, this requires you to log-in in once a month
+
+⚠️ **Only tested on Ubuntu `22.04` w/ Thunderbird version `128.0.1esr`; if you have confirmed this method works on another email client and/or operating system, please update this site or let [Kalum Ost](mailto:[email protected]) know so he may do so** ⚠️
+
+1. Begin to add a new account to your client, as normal, proceeding until you reach the server configurations (this may require you to click a button labelled "Configure Manually" or the like).
+
+2. Change the server type to `IMAP` if it is not already, and the `Authentication Method` to `OAuth2` for both the **Incoming** and **Outgoing** servers. Everything else should be safe to leave alone.
+
+3. Click `Done`; if everything worked correctly, you should see your email synchronize shortly!