Refactor/backend/mail switch to bcc headers

[waveyboym]

Description

This pr introduces some complementary code to complete the moving of mail services to no longer use a test mail but a real email, namely [email protected]. It also moves from using concurrent mail sending to using bcc headers instead

Fixes # (issue)
#335
#310

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Tested with postman to observe expected behavior and worked as expected. The only ensuing problem was that mail went to spam and not to the direct mailbox

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.39%. Comparing base (be356ee) to head (086a187).
Report is 4 commits behind head on develop.

❗ There is a different number of reports uploaded between BASE (be356ee) and HEAD (086a187). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (be356ee)	HEAD (086a187)
	3	1

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #336      +/-   ##
===========================================
- Coverage    79.53%   74.39%   -5.15%     
===========================================
  Files           53       10      -43     
  Lines         3260     1984    -1276     
  Branches        81        0      -81     
===========================================
- Hits          2593     1476    -1117     
+ Misses         578      460     -118     
+ Partials        89       48      -41     

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