Hello,

we are seeing an issue with SOGo contact search when contact display names contain multiple umlauts/diacritics, especially when the name starts with an umlaut (e.g. Ä).

It looks like certain partial search terms do not return the expected contact, even though other partial terms or the full name work.

Expected result:
The contact should be returned for all matching partial queries (prefix / substring search), regardless of umlauts/diacritics.

Actual result:
The contact "Aböabc" can be found with:

• "Ab"
• "Abc"
• "öabc"
• "Aböabc"

But it cannot be found with:

• "Abö"
• "bö"
• "öa"
• "öab"

This is confusing but still workable because the contact can be found with the full name.

However, the issue becomes more problematic when the name starts with an umlaut:

Example contact: "Äböa"

Searching for "Äböa" does NOT return the contact.
Only the following searches return it:

• "böa"
• "öa"