Recently received: a number of suspicious e-mails from following senders
firstname.lastname@example.org with e.g. Subject Chef Kaz relies on Acrobat
Are mails from these addresses reliable, or must I consider them SCAM, SPAM, or other malware?
It is impossible to say if mail is genuine from the sender address. Any address can be faked.
They look like forum notifications. If you don't want them, turn off notifications.