Forwarding from a downstream bug report:
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=233184

Description of problem:

Trying to send /proc/bus/usb/devices as an attachment eventually times out with
a rather hilarious error message:

Cannot append message to mbox file: /home/ajax/.evolution/mail/local/Outbox:
Connection timed out

However, copying the file aside and attaching the copy works just fine. 
/prov/bus/usb/devices is listed as 0 bytes long in ls, so it's probably just evo
getting stuck waiting for zero bytes forever.

Version-Release number of selected component (if applicable):
evolution-data-server 1.11.2
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Based on my observations, at evolution-data-server/camel/camel-file-utils.c is in function camel_read used function select, which waits for max 4 minutes on response from device, and if it will fail (timeout), then the result is an error message mentioned above.