pricerc wrote:Also, if you have a telnet client on the PC (Window Feature option), you can try
- Code: Select all
telnet smtp.sendgrid.net 25
(or whatever your TLS port is). You can just disconnect straight away, but it might also help diagnose the problem.
+1 to this, and also Scott's suggestion if Telnet yields nothing useful to try an email client.
If the DNS resolves, but the connection cannot be established then either something is blocking the outbound (firewall perhaps) or the inbound at the other end (IP blacklisted by the sendgrid network for instance).
SPF, DNSSec and friends probably aren't your issue (would have thought if SPF or DNSSec was a factor you'd get a different sort of error - we just report what the .NET SMTP client throws) - but those might also be a factor - with services like Sendgrid they might be doing something funky outside the RFC standards for SMTP which occurs at the connection level and may explain connection issues also.
EDIT: But given members of the Administrators windows group don't have the issue, then it must be a policy or something on the machine sending - firewall rules should be your first line of inquiry.