How to send email with attachment in jenkinsfile - jenkins

Question

I want to send email after post build action in jenkins. Hence I have write jenkinsfile as follows. But i want to send mail with pdf attachment.
Note: Please don't suggest email plugin procedure & configuration. I preferred Jenkins file method configuration
post {
success {
script {
echo "Success!! e-mailing scan results url to ${emailRecipients}"
mail(from: emailFrom, subject: emailSubjectCDSuccess + COMMIT, to: emailRecipients, body: emailBodyCheckmarx)
}
}
failure {
script {
echo "Failure :( !! e-mailing scan results url to ${emailRecipients}"
mail(from: emailFrom, subject: emailSubjectCDFailure, to: emailRecipients, body: emailBodyCD)
}
}
}

Answer 1

Instead of the default Email step, use the Email Extension Plugin, which allows you to add attachments.
emailext(
subject: "SUBJECT",
attachLog: true, attachmentsPattern: "**/*.txt",compressLog: true,
body: "Test Email" ,to: adress#g.com)

Answer 2

not an answer
try approximately the following parameters of mail step:
def boundary = '----------12345'
def attachment = 'hello world'.bytes.encodeBase64() //read bytes from file and encode as base64
def body = 'hello body'.getBytes('UTF-8').encodeBase64()
mail(
...
mimeType: "multipart/mixed; boundary=${boundary}",
//you can't add extra-spaces or drop empty lines in following string
body: """
${boundary}
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64
${body}
${boundary}
Content-Type: application/octet-stream; name="my-attachment.txt"
Content-Disposition: attachment
Content-Transfer-Encoding: base64
${attachment}
${boundary}--
""".trim()
)