[hammock]

Pontificate in its original sense literally means to perform the duties of a pope or priest (a pontiff). The auto part I guess because it’s email? That part is shakier

[beardyw]

"to speak or express opinions in a pompous or dogmatic way" is I think the intention.

[hammock]

Yes. I didn’t bother to mention that part, only the polysemous connection to pope.

[dfxm12]

Auto as in you get it automatically in your mailbox. No need to ask for it or otherwise seek it out. It's just sent to you.

ETA: other meanings likely don't fit. It's not about self pontificating (well maybe only from Charlie's point of view), and the motorcar related to the Pope is already called the Popemobile.

[bombcar]

Pontoon pontification - bridge building.