A number of general permissions can be set for each group in the Permisions & Limits subsection of the Mail Server module. These settings will also be inherited by all the descendent groups, unless explicitly overridden. If you need to override the inherited settings, untick the Inherit box of the setting and adjust it as appropriate.
Email clients can relay to external domains
Enabling this option will allow users and networks in this group to use third party email software to send mail to external systems. This option should only be enabled for internal networks and users with strong passwords. Allowing users with weak passwords to relay from external addresses could turn your system into a spam relay!
Networks in this group never need to authenticate
Authentication is usually required when relaying email to external addresses from third party email software. Enabling this option will remove the requirement for networks in this group to be authenticated when they send email - this is typically required where the Opendium system is relaying mail from another internal mail server, such as Microsoft Exchange. Please be aware that incorrect configuration can turn your system into a spam relay!
Bypass All Mail Restrictions
If either the sender or recipient of an email has this option enabled, emails will not be restricted by any mail filtering at all, irrespective of any other settings.
Users Can Send Mail to Entire Groups
Senders who are in a group that has this option ticked can send an email to an entire user group. For example, if you have a user group called Staff then an email to email@example.com would be distributed to all users within that group.
Since this gives people the ability to email a potentially very large number of people at once, we recommend only enabling this for a small number of trustworthy users.
Users Can Only Send and Receive Internal Mail
Users or networks who are in a group that has this option ticked are not allowed to send or receive email to or from any external address, they can only send and receive email to or from users within your organisation.
Maximum Size of an Individual Mail
It is usually desirable to restrict the maximum email size that a user can send or receive in order to prevent excessively large emails being sent. We recommend setting a size limit of no more than 25MB, since it is unlikely that another email server would accept emails over this size. Please be aware that when a file is attached to an email, it usually grows to 133% of its original size, due to the MIME encoding overhead.