Possibly a support issue isn't the best place to post this, as I'm offering help rather than looking for it, but this module doesn't seem to have a handbook page, or any other user-editable documentation, so I can't post it there. Maybe if it acquires one in the future, this could be added there.
Anyway, my organization had to try and figure this out recently, and thought I should share what worked for us - a two-part solution.
Part 1: The SMTP module, on its own, won't handle Ubercart e-mails (receipts, order notifications to admins, etc.). So another developer I work with found that installing the Mail System module allowed him to specify SMTP as the mail system for the various types of mail Ubercart sends (basically, it allows more granular control over what kinds of e-mails use what mailing system. So that will allow this module to work with Ubercart!
Part 2: The only problem is, just setting the Ubercart e-mails to use SMTP has the undesirable side effect of stripping out all the formatting, leaving all the text jumbled together in one big barely-readable block. It took some experimenting to find the answer, but what worked was this: In the Mail System settings, scroll down past the class settings to New Class, and create a class that uses UbercartMailSystem as the formatter and SmtpMailSystem as the sender. Voila - sending by SMTP, with Ubercart formatting intact!
Just thought I'd leave that here in case anyone else is having trouble with the same thing. I posted something similar to the Mail System issues queue, but then realized that some people trying to get SMTP to work with Ubercart might not know about Mail System, so they wouldn't get that far... So posting it here as well seemed like a good way to make sure anyone trying to sort this out would find it. Hope that's OK.
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