Hi Martin,

I'm not authoritative on PII policies at all, but here's a couple of things that came to mind as I read your question.

2018-02-10 11:26 GMT+00:00 Martin Urbanec <martin.urbanec@wikimedia.cz>:
To prevent this tool from spamming I of course require its confirmation by accessing an URL with a random string (MD5 hash of user's email and random number from 1 to 100; I mean, those two things are in one hash).

Does this mean the URL for a given email address can be guessed in at most 100 attempts by someone who doesn't control the address? I think you'd typically want to draw your random numbers from a much larger range, or use as token something that was encrypted or signed with a secret only your server knows. It would probably also make sense to make your URLs valid for only a certain time.

Should I stop with collecting mails at all and use some WMF-maintained service for mass-emailing (mailman at lists.wikimedia.org maybe?) and make the tool to just send an email to the list itself? 

If creating a single mailing list is an option (for instance, you don't plan on customizing the emails per user), this seems like a very good way to go.

This question came to my mind before creating, so I do appologize for asking after programming. 

Best regards, 
Martin Urbanec
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