I've had the same network service error which has stopped me from sending and I assume receiving emails.
This has been persistent since the 24 of this month, I'm in the middle of things and need assistance, thanks.

The error log,

method: SendMsgRequest
msg: system failure: IOException
code: service.FAILURE
detail: soap:Receiver
trace: btpool0-3670:1277598087466:1c748c0ff55666f8
request:

Body: {
SendMsgRequest: {
_jsns: "urn:zimbraMail",
m: {
e: [
0: {
a: "duhast@hush.com",
add: 1,
t: "t"
},
1: {
a: "hey-awulor@lycos.com",
t: "f"
}
],
idnt: "13945764-9247-4d96-9ae5-18ec0b08529f",
mp: [
0: {
content: {
_content: "test"
},
ct: "text/plain"
}
],
su: {
_content: "test"
}
},
suid: 1277598068359
}
},
Header: {
context: {
_jsns: "urn:zimbra",
account: {
_content: "hey-awulor@lycos.com",
by: "name"
},
authToken: "(removed)",
format: {
type: "js"
},
notify: {
seq: 67
},
sessionId: {
_content: 116073,
id: 116073
},
userAgent: {
name: "ZimbraWebClient - FF3.0 (Win)",
version: "5.0.18_GA_3028.CentOS5"
}
}
}