Sage 100

Client on Sage 100 Advanced v2015. One workstation keeps getting intermittent electronic delivery errors with ""Unable to login to SMTP connection, Chilkat Log ..."" Have uninstalled and reinstalled workstation, and reset up the email tab in Company Maintenance. It worked a couple times fine, then problem started again. What can I try next?

Does it only happen when certain Senders are e-delivering? What SMTP client are they using? I typically use SMTP Relay to authenticate as one user to make sure the ""hand-shake"" is firm. Then, point Sage to that.