The TO field is similar to an email address and might look something like 2E0SIP@GB7RDG.#42.GBR.EURO.

Broken down this looks like:

2E0SIP - The recipients call sign
GB7RDG - The recipients Home BBS, where the send and receive mail.
#42    - The region ID (See Hierarchal Routing for more)
GBR    - Great Britain
EURO   - Europe

Likewise the From field will be in the same format, directing replies back to the sender.

A personal message addressed to an individual amateur. The amateur might have their mailbox on the same node, or it could be another node several hops away.

Bulletins are for general reception. They could be announcements, weather reports etc. They could be sent World Wide (@WW) or it's possible to direct them to a particular region e.g @EURO for all of Europe, or @GBR.EURO for Great Britain.

A flood bulletin should be “flooded” (sent) to all the local BBSs in the area. For example, someone in Great Britain sends a bulletin to @GBR.EURO. It should be flooded to all the locally reachable BBSs that are also in Great Britain, and likewise they should do the same. It should not be forwarded to any BBSs outside of the region, e.g @FRA.EURO

A directed bulletin is a bulletin that's still in transit, and hasn't reached it's target area yet. For example, an Amateur in the United States might have sent a bulletin to @EURO. Whilst it's being forwarded between nodes in the US it's considered a directed bulletin and won't be flooded to local BBSs, only forwarded to the next route that can reach Europe. Once the bulletin arrives in Europe it would be considered a Flood Bulletin, and will be sent to all local BBSs in that region.

To get a message from the sender to recipient it might have to traverse several nodes. There's no DNS look ups or globally connected internet in packet, so each node needs to know how to route mail to get it closer to the intended destination. To simplify this, Hierarchical Addressing breaks things down into regions.

Take the following simplified example where we assume GB7ASH can reach other nodes in Great Britain, and F8CAL can reach other nodes in Europe:

GB7ASH (Ashford, Kent) <--> GB7DOV (Dover, Kent) <--> F8CAL (Calais, France)

GB7DOV can reach Europe via F8CAL in France. Rather than configuring a route for every BBS or Country in Europe, a rule can be added to forward all messages destined for EURO to F8CAL. This route would also match messages sent to DEU.EURO (Germany), or NLD.EURO (Netherlands) and so on. Likewise in the other direction the SYSOP of GB7DOV can add a rule to direct all messages to GBR.EURO to GB7ASH.

Packet Nodes will always use the most specific match when forwarding mail, so if someone on GB7DOV were to send a message to 2E0SIP@GB7RDG.#42.GBR.EURO, it will follow the GBR.EURO route to GB7ASH and not the less specific EURO route.

Lets take another, more localised example. Assume that GB7WAT can reach other nodes in Great Britain, and GB7HAR can reach other nodes in Essex

GB7WAT (Watford, Hertfordshire) <--> GB7STA (St Albans, Hertfordshire) <--> GB7HAT (Hatfield, Hertfordshire) <--> GB7HAR (Harlow, Essex)

The routing rules would look something like:

GB7WAT

GB7STA

GB7HAT

GB7HAR

The various country identifiers used for Hierarchal Routing can be found in this document:

packet_country_identifiers.pdf

Mirrored from tapr.org

The various UK Regional identifiers used for Hierarchal Routing can be found in this document:

ax25_bbs_uk_forwarding_regions.pdf

Mirrored from G4APL's site