Subscribed e-mails go to spam on GMail

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I'm using answers.ros.org that seem to have upgraded to v0.7.48 recently. Probably since then, e-mail notifications from the web site starts going into spam folder on my GMail. I can't tell why GMail does that, but this might be something I wanted to report, and ask if there's already any workaround.

Update) I found that GMail complains that the smtp server domain that my e-mail address uses is found spammy by them, which seems to mean the cause might not be on askbot-powered server's side? But then why does this issue suddenly start coincidentally with server software update...