{"log":"Traceback (most recent call last):n","stream":"stderr","time":"2018-02-23T09:09:57.667263125Z"}
{"log":"  File "/app/redash/tasks/general.py", line 57, in send_mailn","stream":"stderr","time":"2018-02-23T09:09:57.667267178Z"}
{"log":"    mail.send(message)n","stream":"stderr","time":"2018-02-23T09:09:57.6672709Z"}
{"log":"  File "/usr/local/lib/python2.7/dist-packages/flask_mail.py", line 491, in sendn","stream":"stderr","time":"2018-02-23T09:09:57.667274554Z"}
{"log":"    with self.connect() as connection:n","stream":"stderr","time":"2018-02-23T09:09:57.667280032Z"}
{"log":"  File "/usr/local/lib/python2.7/dist-packages/flask_mail.py", line 144, in __enter__n","stream":"stderr","time":"2018-02-23T09:09:57.667283497Z"}
{"log":"    self.host = self.configure_host()n","stream":"stderr","time":"2018-02-23T09:09:57.667293094Z"}
{"log":"  File "/usr/local/lib/python2.7/dist-packages/flask_mail.py", line 158, in configure_hostn","stream":"stderr","time":"2018-02-23T09:09:57.667296767Z"}
{"log":"    host = smtplib.SMTP(self.mail.server, self.mail.port)n","stream":"stderr","time":"2018-02-23T09:09:57.667300698Z"}
{"log":"  File "/usr/lib/python2.7/smtplib.py", line 256, in __init__n","stream":"stderr","time":"2018-02-23T09:09:57.667304203Z"}
{"log":"    (code, msg) = self.connect(host, port)n","stream":"stderr","time":"2018-02-23T09:09:57.667307718Z"}
{"log":"  File "/usr/lib/python2.7/smtplib.py", line 316, in connectn","stream":"stderr","time":"2018-02-23T09:09:57.667311177Z"}
{"log":"    self.sock = self._get_socket(host, port, self.timeout)n","stream":"stderr","time":"2018-02-23T09:09:57.667332487Z"}
{"log":"  File "/usr/lib/python2.7/smtplib.py", line 291, in _get_socketn","stream":"stderr","time":"2018-02-23T09:09:57.667336556Z"}
{"log":"    return socket.create_connection((host, port), timeout)n","stream":"stderr","time":"2018-02-23T09:09:57.667339622Z"}
{"log":"  File "/usr/lib/python2.7/socket.py", line 575, in create_connectionn","stream":"stderr","time":"2018-02-23T09:09:57.667342548Z"}
{"log":"    raise errn","stream":"stderr","time":"2018-02-23T09:09:57.667345634Z"}
{"log":"error: [Errno 101] Network is unreachablen","stream":"stderr","time":"2018-02-23T09:09:57.667348597Z"}
{"log":"[2018-02-23 09:09:57,668][PID:1][INFO][MainProcess] Task redash.tasks.send_mail[0c83a5cb-c1ec-450d-9c65-0828e0cf9e4e] succeeded in 0.00404308699945s: Nonen","stream":"stderr","time":"2018-02-23T09:09:57.66884594Z"}
{"log":"[2018-02-23 09:09:57,670][PID:1][INFO][MainProcess] Received task: redash.tasks.record_event[4465cd66-e4cf-4619-861b-ed32a9911a95]n","stream":"stderr","time":"2018-02-23T09:09:57.670527622Z"}
{"log":"[2018-02-23 09:09:57,677][PID:1][INFO][MainProcess] Task redash.tasks.record_event[4465cd66-e4cf-4619-861b-ed32a9911a95] succeeded in 0.00623477400222s: Nonen","stream":"stderr","time":"2018-02-23T09:09:57.677343061Z"}

REDASH_MAIL_SERVER: "172.16.21.10"
REDASH_MAIL_PORT: "25"
REDASH_MAIL_DEFAULT_SENDER: "redash-test@hogehoge.com"

CentOS 7.4
IP 172.16.21.10

redash version 3.0.0.b3134
Docker version 18.02.0-ce, build fc4de44
docker-compose version 1.19.0, build 9e633ef

echo test | mail -s "test" -S "smtp=smtp://172.16.21.10:25" me@hogehoge.com