This setting determines if messages that are crossposted are rejected by Lyris, or if they are allowed onto the list.
A cross posted message occurs when a single message is to more than one mailing list on a Lyris server. For example, in the To: field of an email message, the author can list several mailing lists,
and thus deliver the same message to several lists.
By default, Lyris does not allow cross-posting. It will catch a cross-posted message, see that it has already been posted to another list, and reject any further attempts to post the identical
message. If the message is modified slightly in some way (i.e.: an extra space, a carriage return, an extra sentence, etc), it will not be considered a cross posting.
In general, cross-posting to mailing lists is considered bad Internet etiquette, and occasionally, it is a method used by spammers to disseminate inappropriate email. However, there are many
circumstances where it is appropriate. For instance, if there are two mailing lists that deal with related topics, when messages appropriate to both groups are written, the author may want the
message to be distributed to both mailing lists.