[Merge] lp:~bhavesh-goyal093/mailman/Fixed_Bug into lp:mailman

Bhavesh Goyal has proposed merging lp:~bhavesh-goyal093/mailman/Fixed_Bug into lp:mailman. Requested reviews: Mailman Coders (mailman-coders) For more details, see: https://code.launchpad.net/~bhavesh-goyal093/mailman/Fixed_Bug/+merge/251886 Fixed Bug # #1425359 which caused postorius to show 500 error code instead of 409 when same but case sensitive email addresses are entered into subscription list. Earlier : 500 error code when email addresses such as xyz@gmail.com and xyz@Gmail.com are entered which are same Now: 409 error code in both cases since they are same -- Your team Mailman Coders is requested to review the proposed merge of lp:~bhavesh-goyal093/mailman/Fixed_Bug into lp:mailman.