Barrylev, I had the same problem - a setup which was working properly just stopped. I received a message from gmail saying that I tried to use an insecure app. I was quite ill at the time so just reverted to using the gmail webmail app.
I found the latest version of Pmail and loaded it and followed all the steps to make the link with gmail, but still no dice. I then received another message from gmail saying that someone had tried to login to my email account using an insecure non-google app. It also advised that I could allow this connection by altering the security setting in my google account to allow connection to less secure apps. I'm not sure if this is google being incredibly fastidious re security, but I have a sneaking suspicion they might be trying to squeeze out third parties - they even mention MS Outlook as a possible insecure app.
Anyway, I enabled the less secure access and all seemed to fly. Hope this is OK for you and that the lowered security doesn't cause problems.
I too would be keen to learn if there's any other way around google's block.