I didn't get any forum activation link
Lately we’ve had problems with Google randomly locking the account used to send mail, then unlocking it upon request, to then just lock it again a few days later. There’s no explanation as to why this happens now, after years of having used the same setup.
For now we’re instead using MailGun. This has the benefit that mail get sent in a structured manner, but the downside that the mail might become spam classed or outright blocked. This since mail are sent from a shared IP, which might become blocked due to spammers having sent via that same IP.
Anway, if you don’t get notifications as expected, first check your spam folders. If it isn’t there either, it’s possible your email provider outright blocked the mail. You can then try to use a different email address.
It’s possible a better solution will be needed in the longer run, but this will have to do for now.