I know.  Sigh...

Many non-commercial offerings from ISP's have some form of port limitations that are difficult to know, a priori.  That is, until you bump into them.  SMTP comes to mind for Verizon (or maybe it was Optimum Online).  TOMMYT:: sent out-going SMTP for years until it couldn't.  I used that to email myself alerts from Batch.  Now?  Fuggetabout it.

Of course, when I whined about the outgoing SMTP block, I was promptly offered a commercial account...  These cost more then the residential offerings, sometimes far more if you are looking to get equivalent performance.  Really, the residential offerings seem largely geared towards entertainment; that is, watching Netflix and YouTube.  Anything else is bring your wallet.

Standard SNMP can be a security issue.  Even if you are using it only to read values, it constitutes an attack surface from which you can extract information to potentially vector an exploit.  I would imagine that another thing that could be done would be to tunnel it over ssh for point to point solutions.