[exim] full spool

Owing to an unfortunate accident, my disk filled.

What I see in the mainlog is:

2015-11-03 08:05:15 1ZtWah-0007oI-AP Message abandoned: Spool write error (No s\
pace left on device) while receiving message from xxxxxxxxxxxxxxxxxxx [xxx.xxx.\
xx.xx]

I can't find this in the documentation, and there's nothing else about
these messages in mainlog or rejectlog - when does this happen? Does
the transmitting MTA get a 4xx error? Or its connection get closed
silently? Or what?

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