Summer Greeting Card (shochuu mimai)
C: Summer Greeting Card
K: I was able to write this summer greeting card addressed to you, so I’ll send it out!
Y: It’s fine if you give it right now...
C: It was inside your home's mailbox!
Card: How are you doing during this heat? From Koupen-chan.
(an arrow pointing to a drawing of watermelon): I'll give it to you
Translation Notes
From original translation tweets.
郵便受け (yuu-bin-uke) means mailbox. omimai (おみまい) has multiple meanings, such as a get-well letter, an expression of sympathy, or an inquiry to someone's well-being.
In this case, it's like a summer greeting card to ask how someone's doing during the intense heat (sho chuu [o]mimai) (暑中見舞い). "yori" (より) at the end means "from".
References
shochuumimai: http://www.romajidesu.com/dictionary/meaning-of-%E6%9A%91%E4%B8%AD%E8%A6%8B%E8%88%9E%E3%81%84.html
mimai: https://jisho.org/word/%E8%A6%8B%E8%88%9E%E3%81%84
Original Translation Tweets
https://twitter.com/koupenchan_yaku/status/1284319971657433090
https://twitter.com/koupenchan_yaku/status/1285057818005929985
