port 993, is necesary to open it?

Hello, I had a problem with the server today and noticed some kind of denial of service over port 993

I checked #netstat -plan |grep 'ESTABL' and got a lot of unusual connections to port 993

tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.85.208:46994 ESTABLISHED 15651/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:216.9.248.227:48347 ESTABLISHED 16028/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.80.203:52212 ESTABLISHED 15538/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:216.9.249.32:56477 ESTABLISHED 15662/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.81.144:45997 ESTABLISHED 15539/couriertls
tcp 0 24 ::ffff:74.86.xx.xx:110 ::ffff:189.140.157.14:49711 ESTABLISHED 17716/pop3login
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.72.137:38034 ESTABLISHED 15524/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:143 ::ffff:67.223.69.136:43164 ESTABLISHED 15489/imapd
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.73.38:37825 ESTABLISHED 15521/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.80.153:56221 ESTABLISHED 15589/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.72.127:35437 ESTABLISHED 13088/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.76.59:47411 ESTABLISHED 15565/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.76.59:47412 ESTABLISHED 15575/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.84.83:39503 ESTABLISHED 15540/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:143 ::ffff:206.53.151.114:34679 ESTABLISHED 15599/imapd
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.80.81:49257 ESTABLISHED 15506/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.72.91:54139 ESTABLISHED 15743/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.73.192:52082 ESTABLISHED 15556/couriertls
tcp 0 62780 ::ffff:74.86.xx.xx:110 ::ffff:190.146.241.13:60367 ESTABLISHED 15531/pop3d
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.80.175:52519 ESTABLISHED 15522/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.69.210:34372 ESTABLISHED 13197/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:143 ::ffff:201.245.237.188:1194 ESTABLISHED 15171/imapd
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.68.112:33763 ESTABLISHED 15571/couriertls
tcp 0 756 ::ffff:74.86.xx.xx:2382 ::ffff:201.244.171.79:65047 ESTABLISHED 4358/1
tcp 0 16 ::ffff:74.86.xx.xx:110 ::ffff:190.24.138.106:1783 ESTABLISHED -
tcp 0 0 ::ffff:74.86.xx.xx:2382 ::ffff:201.244.171.79:65054 ESTABLISHED 5086/2
tcp 0 6440 ::ffff:74.86.xx.xx:2382 ::ffff:201.244.171.79:65031 ESTABLISHED 3347/0
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.86.16:39051 ESTABLISHED 15584/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.81.57:45462 ESTABLISHED 15580/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:143 ::ffff:67.223.85.151:36816 ESTABLISHED 15498/imapd
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.69.97:60879 ESTABLISHED 15652/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.84.84:60351 ESTABLISHED 15650/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.68.246:54552 ESTABLISHED 15593/couriertls
tcp 0 4104 ::ffff:74.86.xx.xx:2382 ::ffff:201.244.171.79:65177 ESTABLISHED 10010/3
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:206.53.150.158:43354 ESTABLISHED 15653/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.73.199:49203 ESTABLISHED 15520/couriertls
tcp 0 23 ::ffff:74.86.xx.xx:110 ::ffff:190.232.71.107:12910 ESTABLISHED -
tcp 0 37960 ::ffff:74.86.xx.xx:110 ::ffff:190.24.150.12:49468 ESTABLISHED 17540/pop3d
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:216.9.249.161:48925 ESTABLISHED 15555/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:143 ::ffff:67.223.81.67:60543 ESTABLISHED 15490/imapd
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.68.62:60437 ESTABLISHED 15541/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.73.209:44303 ESTABLISHED 15510/couriertls
tcp 0 0 ::ffff:74.86.13.173:993 ::ffff:67.223.77.130:36187 ESTABLISHED 15507/couriertls
tcp 0 42340 ::ffff:74.86.xx.xx:995 ::ffff:198.228.90.116:50958 ESTABLISHED 16206/couriertls
tcp 0 24 ::ffff:74.86.xx.xx:110 ::ffff:200.13.220.228:49933 ESTABLISHED -
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.78.60:46455 ESTABLISHED 14569/couriertls
tcp 0 2230 ::ffff:74.86.xx.xx:110 ::ffff:189.178.32.60:33396 ESTABLISHED 14262/pop3d
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:216.9.249.197:54553 ESTABLISHED 15496/couriertls
tcp 0 933 ::ffff:74.86.xx.xx:995 ::ffff:200.37.161.41:55934 ESTABLISHED 17058/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:216.9.249.197:54552 ESTABLISHED 15493/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:143 ::ffff:67.223.74.36:36683 ESTABLISHED 15501/imapd
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.69.189:49707 ESTABLISHED 16373/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.72.4:48227 ESTABLISHED 16435/couriertls
tcp 0 0 ::ffff:74.86.xx.xx:993 ::ffff:67.223.68.4:11370 ESTABLISHED 15577/couriertls

Closing port 993 solved the problem and load dropped down.

I traced some of those IPs and they resolve to blackberry.net

67.223.80.203 CANADA ONTARIO WATERLOO 43.467
-80.533 - -05:00
Net Speed ISP Domain
- RESEARCH IN MOTION INC BLACKBERRY.NET

I am not sure why this port is required to be open, my customers still doesn't complain about something wrong with the service.