My email provider intercepts emails addressed to me that my provider considers spam and places them in a spam folder. When I retrieve emails using PM, I don't see anything from the spam folder, and as a result, I miss several emails. This happens frequently. I can access it via webmail, but it's inconvenient to go to webmail separately each time to see if my provider has placed any emails there. So, my question: Can I retrieve the contents of my email provider's spam folder using PM?

Yes, you can, but only by creating an IMAP profile in Pegasus Mail (Tools menu > Imap profiles) using the designated address (of the IMAP server) and the proper port your provider offers for doing so: This will enable all subfolders on your account's IMAP server to be displayed in Pegasus Mail according to the options you set up: It'll show up as another mailbox at the bottom of Pegasus Mail's folder tree view. It will not download the messages to the local Pegasus Mail instance but you may move or copy and also delete them to a local folder if desired so, please check the options provided for configuring your IMAP profile. BTW: It won't do any filtering either.

I disabled spam detection on one of my email providers service. The other didn't allow that so I had to create a filter that forced it to deliver all mail to the inbox. I then trained Spamhalter to detect spam as it came into Pegasus Mail. Unfortunately, Spamhalter works in such a way that you can't auto-delete any spam-detected messages so I created filters at my provider to auto-delete the particularly nasty and vulgar messages. The IMAP suggestion made by @idw (Michael) is probably easier unless you are comfortable with filtering and with Spamhalter.