Please Help,

E-mail stopped working after a reboot.
When Outlook starts it appears to connect to Exchange, (the arrow icons on
the folder shortcuts pop up ok) but there is no new mail.
Over night, with Outlook running a few error messages were generated about
not being able to synchronize folders and network connectivity problems.
Internal mail. It sits in the outbox for a minute then seems to go, but
doesnt show up in the recivers box for about a day. Scanmail on the server
reports finding it in the receivers mailbox right away. eventually it does
appear in the receivers mailbox.
Incoming Mail. not getting any. No errors from the POP3 connector. The SMTP
Virtual Server PreSubmission Queue had about 30 e-mails stuck there, all
addresed to users here, all from a 2 minute span about the time of the
reboot.
Outgoing mail stays in the outbox longer than usual, then dissappears. It
does not actually get sent.

All other network functions are OK.

SBS200, Win XP and W98 Clients W/ Outlook 2000
2 nics, router. SMTP out, POP3 Connector in
Trend Scanmail, OfficeScan
GFI Mail Essentials

Have searched newsgroups and MS knowledge base. No luck so far.

RPC connectivity: Used rcpings from server and Client. seemed ok

Events at bootup:
Application log:

Event Source: MSExchangeDSAccess
Event Category: Topology
Event ID: 2104
Description:
Process INETINFO.EXE (PID=2128). All the DS Servers in domain are not
responding.

Event Source: MSExchangeDSAccess
Event Category: Topology
Event ID: 2102
Description:
Process MAD.EXE (PID=2400). All Domain Controller Servers in use are not
responding:
dell.habitat.local

The second one is apparantly Ok to ignore not sure about the first one.

Other recent changes:
Reason for reboot : problems with an Access Database backend on the server.
Shortly after reboot a user noticed slow file transfer speed:. Changed WS
NIC from Half-Duplex to Full Duplex, fixed slowness.
A few days ago replaced a hub with a new switch.

Any Ideas?

Thanks,