In previous posts I have talked about situations where your end users are unable to send or receive email messages under different scenarios. I also posted about the various solutions to those problems. There are a variety of problems and conditions which can create these situations.

One situation where your end users cannot receive email messages but are able to send email involves the configuration of the Exchange server.

Sometimes your end users will come to you and say that they have received the following error message when they try to connect to send email from Outlook or a POP3 (Post Office Protocol) client:

“Messages can be received but not sent. SMTP server unavailable.”

(SMTP stands for Simple Mail Transfer Protocol and is a well known email industry standard. SMTP is used for outgoing mail transport and uses port 25.)

They may also get a variant of that error message such as:

“An unknown error has occurred. Account: ‘SMTP’, Server: ‘Servername’, Protocol: SMTP, Server Response: ‘421 incorrect.domain.com connection limit reached’, Port: 25, Secure(SSL): No, Server Error: 421, Error Number: 0×800CCC67 “

Sometimes you will also see an IP address. The SMTP address, server name and IP address will be different and depend on how your Internet Service Provider (ISP) and email server have been configured.

Continue reading Managing Your Inbound Connections