For a couple of weeks I am having an issue with out exchange 2013 servers.
we have two exchange 2013 CAS servers and two Exchange 2013 mailbox servers. email to the internet is routed through cisco IronPort located in the DMZ. emails to the partner domains is routed directly through wan links and there are connectors for the partner domains.
we are receiving complaints from users that mails are not being delivered from partners domain to out domain and the some users have provided evidence of that. but when we test emails seems to be going but with some delay. it looks like emails with attachments are having issues more that emails without attachments. some emails are missing and not all mails.
there seems to be some problem now since a few days that emails sent to Hotmail are going in spam and some times emails to domains like Gmail are not being delivered (Authentication errors).
there has been no change from our side and now we are having all these issues.
as far as the dns name registration is concerned we have mx records configured only without spf records and it has been like this since the beginning. and we had no issues. fixing the spf records is gonna take time as we have to go through the HO.
I have this issue and lots of tickets related to these issues. any suggestions highly appreciated.