"Business" email letter opening when their signed name is their language center?

How do I respond and open the letter when they're signing their emails with their language center name instead of their "person"-name?

They close with "「ｘ」センター"

Thanks!

Answer

ご担当者様 is the equivalent of "to someone it may concern". You can use it like this:

Xセンター
ご担当者様


お世話になっております、……

From a dictionary:

組織などに手紙や電子メールを送る際、対応する個人名が不明な場合に宛名として用いられる表現。「担当者さま」に丁寧の「ご」をつけた表現。