This occurred last night around midnight. Continued for about 20 minutes then cleared up on it's own. Internal mail was still processing between sessions in webmail. Where do I look for more detail?

 

23:55:18 [192.168.1.10][3631778] connected at 1/11/2017 11:55:18 PM
23:55:18 [192.168.1.10][3631778] "421 Server is busy, try again later." response returned.
23:55:18 [192.168.1.10][3631778] IP is blacklisted
23:55:18 [192.168.1.10][3631778] disconnected at 1/11/2017 11:55:18 PM
23:55:18 [192.168.1.10][19423415] connected at 1/11/2017 11:55:18 PM
23:55:18 [192.168.1.10][19423415] "421 Server is busy, try again later." response returned.
23:55:18 [192.168.1.10][19423415] IP is blacklisted
23:55:18 [192.168.1.10][19423415] disconnected at 1/11/2017 11:55:18 PM
23:55:18 [192.168.1.10][7976794] connected at 1/11/2017 11:55:18 PM
23:55:18 [192.168.1.10][7976794] "421 Server is busy, try again later." response returned.
23:55:18 [192.168.1.10][7976794] IP is blacklisted
23:55:18 [192.168.1.10][7976794] disconnected at 1/11/2017 11:55:18 PM