Add redundant mailbox

[codecov[bot]]

Codecov Report

Merging #163 (046f1b5) into master (21a43bd) will decrease coverage by 0%. The diff coverage is 100%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #163 +/- ## ===================================== - Coverage 86% 85% -0% ===================================== Files 31 31 Lines 4074 4083 +9 Branches 4074 4083 +9 ===================================== + Hits 3463 3468 +5 Misses 597 597 - Partials 14 18 +4 ```

[github-actions[bot]]

Against master [hash=64; threads=1]: 🆗 Elo difference: 6.95 +/- 23.65, LOS: 71.77 %, DrawRatio: 27.67 %

[github-actions[bot]]

Against v1.4.0 [hash=64; threads=1]: 🆗 Elo difference: 2.90 +/- 23.40, LOS: 59.58 %, DrawRatio: 29.17 %

[github-actions[bot]]

Against v1.4.0 [hash=256; threads=4]: 🆗 Elo difference: 24.36 +/- 41.34, LOS: 87.67 %, DrawRatio: 27.00 %

[github-actions[bot]]

Against master [hash=256; threads=4]: 🆗 Elo difference: -3.47 +/- 39.23, LOS: 43.09 %, DrawRatio: 34.00 %