Sqlite - Limit Characters for different parts of one String with Check
So i figured out how to do exactly what i wanted to do.
I used substrings and limited the characters for each individual part of the EMail.

CREATE TABLE User(
EMail varchar NOT NULL COLLATE NOCASE check( (substr(EMail, INSTR(EMail,'.')+1) NOT GLOB '*[^A-Za-z]*') 
AND (substr(EMail,1, INSTR(EMail,'@')-1) NOT GLOB '*[^A-Za-z0-9]*')
AND (substr(EMail, INSTR(EMail,'@')+1, ((INSTR(EMail,'.')-1) - (INSTR(EMail,'@')+1))+1 ) NOT GLOB '*[^A-Za-z0-9]*') 
AND EMAIL LIKE '%_@%_.%_')