Authenticated senders must use valid sender address
If this is selected, users with authentication to send email must configure their email client with a valid email address that is assigned to the mailbox they are using to send on. This option is useful to force clients to use a legitimate email address, thereby reducing the possibility of spam.
Senders from local domains must authenticate to send email
When selected any user sending mail must not only have a valid sender email address it must also have authenticated with a valid MailEnable password for the account. This will help stop any spam coming into the server where the senders address is a local server account. This option is ignored if the sender is sending from a local IP address. If using a sender address which does not include the @ symbol (a non-routable address), then the whole address is checked against the local domain list.
Hide IP addresses from email headers
By default, the IP address of a client connecting is displayed in the header of an email message. If the network has its own IP range which is to remain hidden to receivers of emails, this option will replace the IP address with 127.0.0.1
Require PTR DNS entry for unauthenticated connections
If an inbound connection has not been authenticated, MailEnable will look up to see if there is a PTR DNS entry for the connecting IP address. MailEnable will not validate whether the entry is valid, it will check to see if one exists. Local IP addresses are not checked for PTR entries.
Disable all catchalls
Catchalls for domains will cause the email server to collect a lot more email and can cause the server to relay spam (i.e. if the server redirect a catchall to a remote email address). This option will stop all catchalls from working.
Allow domain literals
MailEnable will allow inbound emails to be formatted as user@[IP Address], such as user@[192.168.3.10]. MailEnable will accept emails for any of the IP address that have been configured on the server. If you are using NAT, or wish to accept extra IP addresses which are not configured on the server, select the 'Advanced' button that will allow these extra IP addresses to be entered.
Use alternate welcome message
When an email client or other mail server connects to MailEnable, a one line welcome message is displayed. By default, this indicates that the server is running MailEnable software, and shows the version of the software. If this option is enabled, it is possible to customize the welcome message. There are also two variables that can be used in the welcome text that will be replaced. These are:%LOCALDOMAIN% - this will be replaced with the SMTP domain from the SMTP options%TIME% - this will be replaced with the current time on the server
Restrict the number of recipients per email
It is possible to restrict the number of recipients per incoming email. Allowing a large number of recipients per message may help with sending to contact lists via email clients, but it also raises the benefit to spammers, as they can save on bandwidth and can send through more messages in a shorter amount of time.
Drop a connection when the failed number of commands or recipients reaches
Most email clients will recognize error codes returned by the mail server for an invalid recipient or similar. But some spammers and bulk email utilities may not recognize these errors and keep trying to send. By enabling this option, MailEnable will drop the client connection. It is recommended not to use a low value (5 for example), as some valid web scripts will not check the return codes either – but these will only produce a small amount of failed commands.
Add to denied IP address if this number is reached
If a connection has reached the disconnection limit, it is possible to automatically add the IP address of the client to the SMTP Access Control list. Be aware that if enabling this option, the Access Control list can grow and adversely affect the performance of the SMTP service. Therefore it is recommended to check the Access Control list regularly.