How to debug mail package



I have a smtp server that accept no secure connections, I set:
export MAIL_URL="smtp://USER@PASSWORD@HOST:25/"

however my app complain about certificate

Exception in callback of async function: Error: certificate has expired
at TLSSocket. (_tls_wrap.js:1103:38)
at emitNone (events.js:106:13)
at TLSSocket.emit (events.js:208:7)
at TLSSocket._finishInit (_tls_wrap.js:637:8)
at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:467:38)

so the question how can debug/fix this problem?