Send email via SMTP server task

mail/OWNERS

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+approvers:
+- akihikokuroda
+- ncskier
+reviewers:
+- akihikokuroda
+- ncskier

mail/README.md

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+Send a message via SMTP server
+
+This task sends a simple email to receivers via SMTP server
+
+## Install the Task and create a secret
+
+```
+kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/master/mail/sendmail.yaml
+```
+
+Create a secret that has the SMTP server information
+
+* **url**: The IP address of the SMTP server
+
+* **port**: The port number of the SMTP server
+
+* **user**: User name for the SMTP server
+
+* **password**: Password for the SMTP server
+
+* **tls**: The tls enabled or not ("True" or "False")
+
+Example server-secret.yaml
+```
+kind: Secret
+apiVersion: v1
+metadata:
+  name: server-secret
+stringData:
+  url: "smtp.server.com"
+  port: "25"
+  user: "userid"
+  password: "password"
+  tls: "False"
+```
+
+Example kubectl command
+```
+kubectl apply -f server-secret.yaml
+```
+
+## Inputs
+
+### Parameters
+
+* **server**: The name of the secret that has the SMTP server information
+
+* **subject**: Email subject (plain text)
+
+* **body**: Email body (plain text)
+
+* **sender**: Email sender email address
+
+* **recipients**: Email recipients email addresses (space delimited)
+
+## Usage
+
+This TaskRun runs the Task to send an email to the receivers via the SMTP server.
+
+```
+apiVersion: tekton.dev/v1alpha1
+kind: TaskRun
+metadata:
+  name: mail-taskrun
+spec:
+  inputs:
+    params:
+    - name: server
+      value: server-secret
+    - name: subject
+      value: Hi, again!
+    - name: body
+      value: "Tekton email"
+    - name: sender
+      value: "<me@myserver.com>"
+    - name: recipients
+      value: "<him@hisserver.com> <her@herserver.com>"
+  taskRef:
+    name: sendmail
+```
+

mail/sendmail.yaml

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+apiVersion: tekton.dev/v1alpha1
+kind: Task
+metadata:
+  name: sendmail
+spec:
+  inputs:
+    params:
+    - name: server
+      type: string
+      description: secret name for SMTP server information (url, port, password)
+    - name: subject
+      type: string
+      description: plain text email subject
+    - name: body
+      type: string
+      description: plain text email body
+    - name: sender
+      type: string
+      description: sender email address
+    - name: recipients
+      type: string
+      description: recipient email addresses (space delimited list)
+  steps:
+  - name: send
+    image: python:3.8-alpine
+    script: |
+      #!/usr/bin/env python3
+      import smtplib, ssl, os
+      port = os.getenv('PORT')
+      smtp_server = os.getenv('SERVER')
+      sender_email = "$(inputs.params.sender)"
+      receiver_emails = "$(inputs.params.recipients)"
+      user = os.getenv('USER')
+      password = os.getenv('PASSWORD')
+      tls = os.getenv('TLS')
+      message = f"""\
+      Subject: $(inputs.params.subject)
+      To: {receiver_emails}
+      From: {sender_email}
+
+      $(inputs.params.body)"""
+      print(message)
+      if tls == 'True':
+          context = ssl.create_default_context()
+          server = smtplib.SMTP_SSL(smtp_server, port, context=context)
+      else:
+          server = smtplib.SMTP(smtp_server, port)
+      if password != '':
+          server.login(user, password)
+      for receiver in receiver_emails.split(' '):
+          server.sendmail(sender_email, receiver, message)
+      server.quit()
+    env:
+    - name: USER
+      valueFrom:
+        secretKeyRef:
+          name: $(inputs.params.server)
+          key: user
+    - name: PASSWORD
+      valueFrom:
+        secretKeyRef:
+          name: $(inputs.params.server)
+          key: password
+    - name: TLS
+      valueFrom:
+        secretKeyRef:
+          name: $(inputs.params.server)
+          key: tls
+    - name: SERVER
+      valueFrom:
+        secretKeyRef:
+          name: $(inputs.params.server)
+          key: url
+    - name: PORT
+      valueFrom:
+        secretKeyRef:
+          name: $(inputs.params.server)
+          key: port