"You are receiving this email because this is an important message regarding your account and products you are using. You are not allowed to unsubscribe from this type of message."
Edit: To all the concern trolls who think the contents of the email is important context as to whether I'm allowed to be annoyed or not, understand that I am not Atlassian's customer. We have zero active licenses for any Atlassian products.
What was the subject of the email? Because if they are alerting you to some security issue regarding your account, I think it is reasonable to prevent the user from unsubscribing, otherwise how would they be alerting you and would you then blame them for not having alerted you?
Of course, if this is a marketing email, that's something else but then is it an important message regarding your account and products you are using?
I have an email that I guess used to be someone else's and I keep getting emails from their Facebook and Apple iCloud accounts that I can't even unsubscribe from because I need to log in to unsubscribe. It's incredibly annoying, and even a privacy issue which I messaged Facebook about and have been ignored.
Sounds like a reasonable email, and being able to unsubscribe from account-related communication would be a way of evading security measures to a malicious actor.
I had 2 of these just this week. Disney+ sent an ESPN ad with no way to unsubscribe, despite my having all marketing emails turned off. Their chat rep laughably insisted it was not a marketing email, just a way to "help" people use their services. It's very kind of Disney to be looking out for me.
Best Buy sent me a marketing ad with a $5 coupon (lol) attached. All marketing emails were disabled with them too and again there was no way to unsubscribe.
Both problems were easily solved by deleting my accounts.