Not without first exhausting the easy options of figuring out the problem yourself, but otherwise yes, messaging other mail operators at the postmaster mailbox is fine and can help improve things on both ends.
You should do the following first:
- confirm that your own
postmaster and abuse mailbox is reachable and has no outstanding requests/complaints
- ensure you have seen the full status message (generally included in your mail software "bounce" message), not just the first line, displayed in a truncated fashion in a log
- get an overview of all the rejection reasons you have accrued in recent times, the same problem may be reported in different ways by different recipients, maybe a different status message than the one you quoted is more useful to you
- check the recipient address for formatting problems (in effect trying to send to a mailbox starting with a space or quotation mark)
In this case, it appears like the receiving side has configured a rather unspecific SMTP status message and should improve that anyway, regardless of whether the problem you ran into was in fact to be solved on your end. Standard etiquette appears to be to keep your actual request for diagnostic help very clear & concise, yet include everything possibly needed to help you below.
If the problem that caused the message was your fault (buggy software, improper processing of mail addresses, ..) the answer will be in a slightly annoyed tone. If your message is unclear or initially directed to the wrong mailbox your message will likely be ignored. So do make sure your question quotes the relevant information necessary for the other party to check their logs, that is: headers of a sample mail, your logs quoting the precise time and status message received on the delivery attempt, and a general statement about how you are acquiring informed consent before sending something you expect people to manually unsubscribe.
