The optional text that will appear in the subject line. For example, add a “List- ” or “Discussion -” prefix so that users know that the message is posted to an email list. Recipients can then create filters to move those messages to a specific folder or manage them in some other way.

Follow these steps the automatic subject line in mail list

1. Log in to Enterprise Email as the domain administrator.
2. Expand the Domain Settings and Mailing Lists folders.
3. Click Mailing Lists in the navigation pane.
4. Select the Mailing list
5. Click on Subject Prefix tab and mentioned the subject line while sending to mailing list.
6. Click on Allowed Poster and select the Subscribe only.
7. Click Save.

Allowed Poster

Whitelist email addresses or domains who can post to the mailing list

• Allow anyone to post – When enabled, anyone can email the list, regardless of whether they are subscribed to the list or not. In turn, this sends an email to all members. Note: This setting can cause abuse if it is not closely monitored. Therefore, it is recommended to restrict the allowed posters to just subscribers, at the very least.

• Allow subscribers to post – When enabled, allows the list subscribers, and only the list subscribers, to send and receive posts. This can cause abuse issues as well if you have an active list, so this should only be used for smaller lists or for digest mode only.

• List Administrators Only –  Regardless of which option is enabled, List Moderators will always have the ability to post to the list. For particularly large lists, or for very active lists, it is recommended that both options, above, be disabled so only the List Moderator can post to the list as this ensures only relevant information is passed along and there is less chance of abuse.