how to change the select-options fields length to long

Dear friends:

I had develop a program for sent email,and it have a field for fill mail address as below:

data: lmail like adr6-smtp_addr.

select-options: mailadd for lmail no intervals.

my customer complain that the field is too short,but I can not change it to longer,the select-options component limit the visible length , how can i do for this problem!