alan@arcticus:~ $ grep -i "receipt" /var/log/mail.log.1
Feb 14 17:17:23 arcticus sm-mta[7546]: 21EHHBjQ007514: 21EHHNjQ007546: DSN: Return receipt
Feb 14 17:38:14 arcticus sm-mta[12306]: 21EHcAjU012280: 21EHcEjU012306: DSN: Return receipt
Feb 15 13:24:00 arcticus sm-mta[27886]: 21FDNvY7027873: 21FDO0Y7027886: DSN: Return receipt
Feb 16 05:35:17 arcticus sm-mta[26349]: 21G5ZCYq026323: 21G5ZHYq026349: DSN: Return receipt
Feb 18 04:21:29 arcticus sm-mta[31257]: 21I4LO1E031232: 21I4LT1E031257: DSN: Return receipt
Feb 19 05:46:12 arcticus sm-mta[29926]: 21J5k9FF029877: 21J5kCFF029926: DSN: Return receipt
alan@arcticus:~ $