Exchange Mail Defer Reason: LED=450 4.4.318 Connection was - Microsoft Community

split thread.

hello bertel,

kindly note that we have used hybrid configuration wizard (hcw) exchange 2013 office 365, , completed.

this wizard created send/receive connectors, default didn't touch them , didn't edit configuration.

the outbound send connector office 365 on premise server, forward emails our real ip.

and on error mentioned ip: "reason: [{led=450 4.4.318 connection closed abruptly ‎(suspiciousremoteservererror)‎};{msg=};{fqdn=our fqdn};{ip=our real ip};{lrt=7/11/2017 2:47:21 pm}]. outboundproxytargetip: 205.177.180.161. outboundproxytargethostname: our fqdn"

i guess traffic forwarded office 365 our firewalls refused here on our enviroment.

my question is: rules or policies should applied on firewall sides ? opened 25 traffic no luck.

please advise,

thanks in advance,

hassan al kak

hi hassan,

office 365 ip lists may changed , please have check, make sure there no ip address blocked firewall.

reference:

exchange online protection ip addresses
https://technet.microsoft.com/en-us/library/dn163583 

if doesn't work, may know if issue happens when sending emails large group? if yes, try increasing maxrecipientspermessage 5000 (default setting) running following command:

set-receiveconnector -identity “server\name” -maxrecipientspermessage 5000

will work? use fope?

[updated alison wang msft, 8:22, july 22, 2017 (utc)]

best regards,

alison

Office / Office 365 for admins / Exchange Online