fix data race sending mail

[xhit]

Fix #75

[codecov-commenter]

Codecov Report

Merging #82 (fcf2fd2) into master (6250c42) will increase coverage by 20.89%.
The diff coverage is 59.09%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@             Coverage Diff             @@
##           master      #82       +/-   ##
===========================================
+ Coverage   33.09%   53.98%   +20.89%     
===========================================
  Files           7        7               
  Lines        1233     1243       +10     
===========================================
+ Hits          408      671      +263     
+ Misses        799      507      -292     
- Partials       26       65       +39     

Flag	Coverage Δ
unittests	53.98% <59.09%> (+20.89%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
email.go	34.45% <59.09%> (+31.88%)	⬆️

... and 1 file with indirect coverage changes