Adding alt text for the images because this is very serious information everyone should have access to since their accounts could be at risk if they follow these fake instructions:
[Image description: a screenshot of a Tumblr account impersonating Staff with the username "support61871", the blog name "Tumblr staff" and the Tumblr logo as their icon. Their bio links to the real Staff account and profile.
Under the bio there is a post that reads as follows:
"Account Verification Under New Terms of Service
We're writing to inform you about an important change to our security procedures.
Effective immediately, following the updated Tumblr Terms of Service and Community Guidelines (version 2.5.1.), all users will be required to complete identity and account verification.
Recently, we've seen an increase in policy violations – including bot activity, automated content scraping, and unauthorized data access. To protect our community and maintain a safe environment for everyone, we are introducing mandatory verification for all active accounts.
Please click the official verification link below and follow the intructions provided:
[link to a fake verification page posing as real]
We kindly ask that you complete the verification process within 72 hours of receiving this notice. Accounts that are not verified by the deadline may be subject to temporary restrictions until verification is completed.
Thank you for your cooperation and understanding as we work to keep Tumblr safe.
Best regards, The Tumblr Support Team."
Needless to say, this isn't how Tumblr verification works. For starters, it only applies to users from countries with governments that unfortunately require it (because otherwise Tumblr wouldn't be able to operate in those countries; it sucks but they're not the ones calling the shots here). Also, it's done via a third party, k-ID.
This is the real link with instructions and information on how to verify your age. Anything else is a scam or bots trying to steal your account:
https://help.tumblr.com/knowledge-base/verifying-your-age/
As OP said, Tumblr will only contact you via e-mail or official accounts, which don't have a bunch of random numbers in their usernames. Please stay alert and report them!