Here are the basic SSH commands to assist in troubleshooting any suspected 
exim mail server troubles:
 
    - Display the current exim configuration 
exim -bP  
    - List the messages currently in the exim queue  
exim -bp  
    - Count the messages currently in the exim queue 
exim -bpc  
    - Combine a List with sSummary  
exim -bp | exiqsumm  
    - Explain current exim status and function  
exiwhat  
    - Test a mail address  
exim -bt {full-email-address}  
    -  
 
    - Test incoming mail connection as if from an IP 
exim -bh {IP} 
If your mailserver is rejecting mail from a specific location this will allow you to test as if you were at that IP (note any mails created are auto-discarded)