This part of the code contains the code that allows people to subscribe to a group using email. It is analogous to the web-based sign-up system [1] and related to the join system [2]. Signing up using email is done in two phases: the subscribe email-command initially screens the messages coming in, while the confirm email-command ensures that people know what they are getting in for. Three notifications are sent out for various reasons.

The logic behind the Subscribe email command [3] is difficult because it can be sent to a group of any privacy.

• If an existing group member sends a Subscribe email to a group then it is treated as an ordinary email.

• If a person with a profile, who is not a group member, sends a Subscribe email to a public group then a Confirm notification is sent.

• If a person without a profile sends a Subscribe email to a public group then

  • A profile is created, and
  • A Confirm notification is sent.

  The name (fn) of the profile is the display-name in the From address, or the local-part of the address (the left-hand side of the @) if the display-name is not present.

• If a person with a profile, who is not a group member but is a site member, sends a Subscribe email to a public to site-members group then a Confirm notification is sent.

• In all other cases a Cannot join notification is sent.

The Confirm notification is, if anything, uglier than the Subscribe command. The email is designed to be sent back, in order to confirm that the sender wants to join the group. So the subject of the command will start with Re: Confirm; it is for the Confirm command that the Re: is stripped from the start of all the emails.

Each confirmation has a unique six-digit (base 62) identifier. It is shown the end of the subject line for the Confirm command. If stripped the subscription request cannot be confirmed. When checked not only is the confirmation-ID looked up, the email-address is also checked. I am unsure what issues could arise if we let people confirm for others, but it smells dodgy.

If everything checks out correctly then the member is joined to the group, using the normal join mechanism [2]. Otherwise a "Contact us" email is sent. Much can go wrong, and rather than write (around six) separate notifications one message is sent that asks the person to contact Support.

• Confirm: gs-group-member-subscribe-confirm.html
• Cannot subscribe: gs-group-member-subscribe-refuse.html
• Confirmation problems: gs-group-member-subscribe-confirm-problems.html

• Code repository: https://github.com/groupserver/gs.group.member.subscribe
• Questions and comments to http://groupserver.org/groups/development
• Report bugs at https://redmine.iopen.net/projects/groupserver