• split into local+domain  or  keep as one string
• canonicalize before storing  or  when using operators
• fixed-length structure  or  variable length structure

struct Email { char local[128]; char domain[128]; }

Problems: wastes space, buffers too short (129 for '\0')

Better solution:

struct Email { int32 len; int32 dom0; char addr[1]; }

Assumes: copy whole string, convert to lower-case, replace '@' by '\0'