The letter was returned as insufficient postage because its size exceeded the limit for standard-size postal items.
こんにちは!
ご質問ありがとうございます。
『手紙が定形郵便物の大きさを超えてて料金不足で戻って来た』は、
いくつか言い方が考えられますが、
The letter was returned as insufficient postage because its size exceeded the limit for standard-size postal items. と言えます。
メモ
return 返送する
insufficient 不十分な、不足して、不適当な、足りない
postage 送料、郵送料金
exceed limit 枠を超える
standard-size postal items 定形郵便物
参考になれば幸いです。
The letter was returned because it exceeded the standard size and didn't have enough postage.
・**The letter was returned because it exceeded the standard size and didn't have enough postage.**
・**My card came back due to insufficient postage — it was too big for regular mail.**
● **returned**:「戻ってきた」
郵便物が差出人に戻ることは「was returned」で表せます。
例:**The package was returned to me.(荷物が私の元に戻ってきた)**