I have a feeling I'm missing something simple and going to kick myself when someone posts the obvious answer! But I'm not much of a networking guy and inherited the responsibility due to layoffs. So any help would be appreciated.
On Friday morning, we started experiencing some strange network behavior. Some, but not all, users were complaining that they could not connect to Exchange and/or network shares and/or the internet. The users always reboot about 3 times before they contact me, and that usually didn't help. However, while troubleshooting one user's PC, I managed to regain access simply by disabling and enabling his network adapter. (I was finding that the PCs had no IP address when things went south, and were getting a local 192 address.)
About mid-day, the company iPhones started giving a connection error to Exchange, with a message that said something about an untrusted connection or certificate. (I'm sorry, but after you click the message, it doesn't come back so I can't quote it exactly.)
I also noticed that while my PC never lost connection to anything (I had Exchange, shares and internet), I was not receiving any emails from outside the company. Test emails from my personal account never came through, and test emails to my personal account never went out.
Yesterday, I received a delivery notification email from my personal account due to the fact that my test email never went through. The notification included:
Your message has been enqueued and undeliverable for 1 day
to the following recipients:
Recipient address: firstname.lastname@example.org
Reason: unable to deliver this message after 1 day
Delivery attempt history for your mail:
Sat, 27 Jun 2015 23:07:13 +0000 (GMT)
TCP active open: Failed connect() to TCP port 25 of 173.xx.xx.xx (No formatted text for errno = 110)
The IP mentioned in the notification is our static public address for mail.
If it helps, our basic network: Internet -> Comcast modem -> Cisco ASA5510 -> HP switch/network. Our DC provides DHCP.
Hopefully I've included enough information. I'm hoping someone can point out the obvious that I'm missing. Thanks.