It is more likely, that GMail is blocking the older TB browser. They always complain about our Firefox, when I use that with their web access, but they still allow the older one to work, after I specifically select the option.
FWIW, I use PMMail, which will only use POP3 (and SMTP, for sending). It works okay with the GMail server (after extensive setup), but I can't see what they (often incorrectly) move to their SPAM folder, without logging into the web interface. They also track everything that I do, and I am convinced that they are the cause of a recent surge in SPAM mail. I am not very happy with Telus, or GMail, because neither one of them will respond to my request that they stop filtering my mail, and saving my information on their servers.
I have been looking into opening my Weasel mail server (I use it for testing PMMail), but I can't seem to get the modem to open the ports. My new router (tp-link Archer C7) does it properly, so I expect that my ISP (Telus) is blocking things. My next approach is to change the external ports, but I haven't tried that, yet.