If you want to use the possibility to forward mails from an external mail address to another mailbox, then please note that this is not possible when using our mail service.
The reason for this lies in the way how forwarding by default works. The original mailserver will send a mail using the SPF-record of the sender domain which will probably have authorized that server. The problem is that when a mail is forwarded (by our servers), the IP of the mail service will be seen as the sending server by the receiving mail server.
If for example someone mails from a gmail-address, the mail servers IP-addresses will not be listed in the SPF-record for gmail.com so our server is not authorized. In most cases this will result in either a bounce or a marking as 'unwanted'.
Why do you not have support for this?
SRS is in theory a great technique, but the implementation in a lot of mailserver software is still lacking or pretty difficult to configure. Because of this we have decided during the test-phase that we will not official support this, as we can not guarantee it working successfully in most cases.