Updated the development guide - https://docs.google.com/document/d/1_9C03q6TD5wjLqfVLKsuDsIEQ4-qrS0JhONO5VBOwaA/edit?pli=1&tab=t.0

Main issue causing inconsistency in sending mails locally -

Email Port Differences: Local vs Production

Local Dev: Only port 465 with SSL works. Port 587 hangs due to possible ISP, VPN, or firewall restrictions on outbound TLS connections.
Production: Port 587 with TLS works as expected. Network/firewall policies differ from local environment.

Some comments I had after running through this documentation with Dr. Freese:

Step 10:
#5: The details for setting up a project have been omitted here. Likely because it's straightforward, but since I'm prompted to enter a Project name, I'd like if one was provided in the documentation.
#6-7: I think these can be skipped? When I make a project, I'm sent back to the developers console where there's a button at the top of the Credentials page that says "Create credentials". I can just click this and that is what #8 captures.
#9: There is no radio button now. Instead, a warning has appeared that says, "To create an OAuth client ID, you must first configure your consent screen." And with that warning is a button labeled "Configure consent screen" which is what I need to click next. That should be #9. Then #10 should be the next item which is to configure the Google Auth Platform. There are fields here that should be outlined in the documentation, such as App Information, Audience (internal vs external), etc. After completing this project configuration, now a button is displayed that says "Create OAuth client". This is where the current #9 picks up. Again, when creating the OAuth client ID, I'd like if the Name field could be provided in the documentation (unless you'd like to use the default "Web Client 1").
#12: This is a small point but we did have to search for Google+ API which was confusing to Dr. Freese at first. Might be good to note!

The email set-up does appear to be working consistently now! My only request would be to include a screenshot of what your settings.ini might look like. You can use a fake email/password for documentation purposes, but it's nice to be able to check if I've got all the right lines in that file.

attn Paige Kulzer Nowlan Freese

Changes are done and final document is ready, review the document and let's see if we need anything else to be added.

I'm very happy with the changes! Step 10 might keep evolving in the future since Google seems to be changing things constantly, but everything is up to date and easy to follow.

Closing ticket!