How secure is Google Mail really?

Hi everyone!

I've always wondered how reliable and secure email is. I've read that they scan your emails (not sure about files) to update your ad profile. The thing is, basically all companies I've done business with use Google Mail to send personal data like address and whatnot, both in PDF file and or just plain text, and I wonder if that's not breaching any GDPR rules or anything (some of these companies say that email processes content outside the …

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