SMTP Settings

Options | Outgoing Mail | SMTP Settings-tab

The SMTP settings dialog allows the configuration of additional settings for the SMTP client.

The default host name used in mail server HELO/EHLO conversations can be adjusted here.

HELO name
When a mail server connects to another one to deliver mail, it 'says hello' the other server with its own name.

This should correspond to the internet name of the server.
For example: mail.mydomain.com 
So a DNS lookup to mail.mydomain.com should return the IP address of your server.

Many mail servers perform this check, and if the HELO name does not correspond to your IP address, they reject your mail.

The Local Domain Name is that set in Options | Server

Specify Host Name allows you to set it yourself - mail.mydomain.com

Perform Reverse Lookup will offer as the HELO a match to the lookup by the remote server you are connecting to.

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Limit Recipients Per Message

This dialog allows Administrators to control how many recipients a message may have, and is normally used to control abuse.