mysqldump error:数据包大于max_allowed_packet'

My application download mails over IMAP and stores them in a MySQL database. Earlier I was supporting mails size upto 10 MB and hence a 'mediumtext' column to store the mail content was enough. Now I need to support mails upto 30MB. So I changed the datatype for the column to 'largetext'. Yesterday a mail with size 25 MB was stored. After that whenever I execute mysqldump command it throws error:My application download mails over IMAP and sto