Some users have set up automatic forwarding of their domain hosted email to 3rd party systems such as Gmail.
Laughing Squid cannot guarantee delivery of such messages. In particular, forwarding reliability may be affected by policies set by either the sender's email service/domain settings or by the recipient's email service/domain settings. This means that some messages may be received at your domain based mailbox and forwarded to the destination but not displayed in the destination mailbox. The way this works may change over time as various email providers change their policies. Laughing Squid has no control over this behavior.
If you decide to set up forwarding to an external provider and need to be sure that you don't lose any email, be sure to choose to 'keep a copy' of forwarded messages in your Webmail mailbox. Then, regularly review your mailbox for any messages that may not have been delivered to your destination.