If you are looking for a pool to mine with your Bitmain X3 I have been using Successfully the following:

Bytecoin BCN

URL: stratum+tcp://bcn.superpools.online:9999
Worker: your wallet address (optional +PaymentID for exchange)
Pawword: x

Electroneum (ETN)

URL: stratum+tcp://etn.superpools.online:9999
Worker: your wallet address (optional +PaymentID for exchange)
Pawword: x

Newton NCP

URL: stratum+tcp://ncp.superpools.online:9999
Worker: your wallet address
Pawword: x

B2b

URL: stratum+tcp://b2b.superpools.online:9999
Worker: your wallet address
Pawword: x

Karbo KRB

URL: stratum+tcp://krb.superpools.online:9999
Worker: your wallet address
Pawword: x

Sumokoin (SUMO)

URL: stratum+tcp://sumo.superpools.online:4999
Worker: your wallet address
Pawword: x

Dero (DERO)

URL: stratum+tcp://dero.superpools.online:19999
Worker: your wallet address
Pawword: x