My error message from the sender is: shw-ibgw-4001a.ext.c...

[ivcairns]

My error message from the sender is:

shw-ibgw-4001a.ext.cloudfilter.net gave this error:40.92.42.30 blocked AUP#CDRBL

[rstra]

@ivcairns  That IP address is listed on SORBS sorbs.net, Cloudfilter might be blocking the sender for that reason.

[mdk]

@ivcairns -- note:

Name: mail-mw2nam10olkn2030.outbound.protection.outlook.com
Address: 40.92.42.30

Some spammer/scammer was sending "too-many" messages out from their Microsoft account.

So, the IP-address got black-listed, much to the annoyance of legitimate Microsoft users whose E-mail goes "out" through that server.

There are procedures to get black-list-maintaining sites, such as SORBS, to remove the IP-address from black-list. Hopefully, some other person similarly affected by the black-list entry would already have contacted SORBS.