Following JCL can be used to send attachment in mail using mainframe
//STEP1 EXEC PGM=IEBGENER
//SYSPRINT DD SYSOUT=*
//SYSIN DD DUMMY
//SYSOUT DD SYSOUT=*
//SYSUDUMP DD SYSOUT=D
//SYSUT2 DD SYSOUT=(B,SMTP)
//SYSUT1 DD DSN=USERID.MAIL.FILE,DISP=SHR
// DD DSN=USERID.MAIL.ATTACH,DISP=SHR
CONTENTS OF USERID.MAIL.FILE
HELO FIRSTNAME
MAIL FROM: <>
RCPT TO: <>
DATA
FROM: NAME OF PERSON
TO: <>
CC: <>
SUBJECT: REPORT FILES ATTACHED
MIME-VERSION: 1.0
CONTENT-TYPE: TEXT/PLAIN; NAME="TEST.TXT"
CONTENT-DISPOSITION: ATTACHMENT; FILENAME="TEST.TXT"
CONTENTS OF USERID.MAIL.ATTACH
DATA IN THE ATTACHMENT FILE
DATA IN THE ATTACHMENT FILE
DATA IN THE ATTACHMENT FILE
DATA IN THE ATTACHMENT FILE
DATA IN THE ATTACHMENT FILE
DATA IN THE ATTACHMENT FILE