send_mail(): support plaintext w/o auth

[vetinari]

support plaintext connections to SMTP server when we do not authenticate

[codecov[bot]]

Codecov Report

Merging #402 into master will decrease coverage by 0.04%. The diff coverage is 22.22%.

@@            Coverage Diff             @@
##           master     #402      +/-   ##
==========================================
- Coverage   75.37%   75.33%   -0.05%     
==========================================
  Files          80       80              
  Lines        5946     5952       +6     
==========================================
+ Hits         4482     4484       +2     
- Misses       1464     1468       +4

Impacted Files	Coverage Δ
...n_worker_monitor/zmon_worker/notifications/mail.py	78.44% <22.22%> (-2.47%)	:arrow_down:

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[codecov[bot]]

Codecov Report

Merging #402 into master will decrease coverage by 0.05%. The diff coverage is 25%.

@@            Coverage Diff             @@
##           master     #402      +/-   ##
==========================================
- Coverage   75.37%   75.31%   -0.06%     
==========================================
  Files          80       80              
  Lines        5946     5952       +6     
==========================================
+ Hits         4482     4483       +1     
- Misses       1464     1469       +5

Impacted Files	Coverage Δ
...n_worker_monitor/zmon_worker/notifications/mail.py	78.44% <25%> (-2.47%)	:arrow_down:
zmon_worker_monitor/zmon_worker/tasks/main.py	74.53% <0%> (-0.11%)	:arrow_down:

---

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Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 7c07123...8df2d04. Read the comment docs.

[pitr]

👍

[vetinari]

:+1: