Users cannot access the servers : There have often being cases of IT admins observing that user's aren't able to connect to server.Although there can be various causes for this, the first thing to make sure is to make sure the general network connectivity is working just fine.Some other troubleshooting techniques can involve seeing whether users can connect to some other servers in same switch.
Error 450 4.7.1 : When Email sending fails, this error is returned.There a few notable scenarios that could lead to this error :
-the number of outgoing mails from a particular user is kept capped by the exchange administrator
-reverse lookup operation failed and the exchange server was not able to resolve sender's IP.
-the address to which the the mail delivery is to be attempted is blocked by the exchange.
Mail flow issues : When the most basics of exchange functionality that is sending or receiving mails is affected you know that issue is serious and needs to be dealt with quickly for maintaining mail flow. First off check the most likely factor that could have cause this mini catastrophe of sorts - dns server configuration. 'nsllookup' is a command line utility that can fix DNS errors with ease. Another often advised method for troubleshooting this will be to use the Microsoft mail flow troubleshooter.
Outlook not connecting to exchange : This being the most common of all could be due to more than one factor contributing factor however finding the root cause here isn't that hard. Start off by using the Microsoft Connectivity Analyzer.
Although we have discussed multiple errors and its causes some of these can also occur due to exchange database corruption (.edb file) corruption as well. EDB corruptions can be a big headache for the administrators as it can essentially paralyze the whole exchange setup.
Only a perfect exchange recovery mechanism can work in such scenarios and as such using a tried and tested exchange server recovery tool like EdbMails can be more than advantageous. The EDB to PST Converter from EdbMails is capable of using its deep scanning algorithms to quickly and effectively recover every last bit of information from inaccessible exchange databases.