Method (%Net.SMTP).Send returns error # 6167 (Authentication expected but failed.)

Our client says the call to send email (method (%Net.SMTP).Send) started returning error # 6167 (Authentication expected but failed.) after installing IRIS 2022.1.2; email had worked before. Properties (%Net.Authenticator).UserName and .Password were configured. We can get email to work when we don't set property (%Net.SMTP).authenticator.

Any ideas what is going on? Thanks.