Suddenly cannot receive email from singnet.com.sg
I have my pacbell.net account for decades, and suddenly, people sending email to me from singnet.com.sg are suddenly getting 553 5.3.0 errors. They have no trouble sending email from other domains. This has all the signs that ATT or Yahoo is blocking email from singnet.com.sg. I can't seem to find any support contact to ask them to fix this. Anybody know how to find out what is going on?