A VirtualMTA (also known as a Mail Route) is a path that mail takes to reach its destination. Each VirtualMTA can be classified as one of the three types below:
- IP Address - a single IP address that is used to send messages.
- Relay Server - an SMTP relay server that GreenArrow Engine forwards messages onto. This could be another GreenArrow Engine installation or any other SMTP server that is configured to accept messages.
- Routing Rule - a group of one or more IP Addresses, Relay Servers and/or other Routing Rules. Routing Rules are most commonly used to load balance outgoing messages over multiple IP addresses.
Each message that GreenArrow Engine attempts to send is associated with a VirtualMTA. There are a number of ways in which a VirtualMTA can be specified, depending on how messages are coming into GreenArrow Engine:
- Raw Injection - the
X-GreenArrow-MtaIDheader is used, or relay client IP addresses are statically associated with VirtualMTAs.
- SimpleMH - the
X-GreenArrow-MtaIDheader is used to specify a VirtualMTA, the
X-GreenArrow-MailClassheader is used to specify a Mail Class, or relay client IP addresses are statically associated with Mail Classes. Each Mail Class in turns maps to a VirtualMTA.
- GreenArrow Studio - a VirtualMTA can be assigned to each mailing list.
If no VirtualMTA is specified, or if the VirtualMTA that is specified doesn’t exist, then the message will be sent through the default VirtualMTA of the server.