MailNotifier fails with SMTP error if useTLS=False but buildbot[tls] has been installed.

[mrstanwell]

If I install buildbot and then install the buildbot[tls] bundle, it pulls in dependencies pyasn1 pyasn1-modules pyopenssl service-identity. However, after that, MailNotifier runs start failing due to failure to connect to SMTP server, even though useTLS is not set.

Using:

• Ubuntu LInux 18.04.5
• Python 3.6.9
• buildbot 2.8.4

Steps to reproduce:

1. Create a new virtual environment and activate it.
2. pip install --upgrade pip wheel setuptools
3. pip install buildbot[bundle]
4. pip install buildbot[tls]
5. pip install requests (I need this because I'm using Google Auth)
6. Start buildbot with a master.cfg that has a MailNotifier configured, and do something that triggers the MailNotifier.

Expected behavior:

• Email notification is sent

Actual behavior:

2020-11-02 14:45:46-0600 [-] Starting factory <twisted.mail.smtp.ESMTPSenderFactory object at 0x7f2dd58e5048>
2020-11-02 14:45:46-0600 [ESMTPSender,client] SMTP Client retrying server. Retry: 5
2020-11-02 14:45:46-0600 [ESMTPSender,client] SMTP Client retrying server. Retry: 4
2020-11-02 14:45:46-0600 [ESMTPSender,client] SMTP Client retrying server. Retry: 3
2020-11-02 14:45:46-0600 [ESMTPSender,client] SMTP Client retrying server. Retry: 2
2020-11-02 14:45:46-0600 [ESMTPSender,client] SMTP Client retrying server. Retry: 1
2020-11-02 14:45:46-0600 [-] Stopping factory <twisted.mail.smtp.ESMTPSenderFactory object at 0x7f2dd58e5048>
...
2020-11-02 14:46:25-0600 [-] Unhandled error in Deferred:
2020-11-02 14:46:25-0600 [-] Unhandled Error
    Traceback (most recent call last):
    --- <exception caught here> ---
      File "REDACTED/lib/python3.6/site-packages/buildbot/reporters/notifier.py", line 279, in buildMessage
        list(users), patches, logs)
      File "REDACTED/lib/python3.6/site-packages/buildbot/reporters/mail.py", line 280, in sendMessage
        yield self.sendMail(m, all_recipients)
    twisted.mail._except.SMTPConnectError: Unable to connect to server.

If I uninstall the above listed dependencies installed by buildbot[tls], MailNotifier resumes normal operation.

Am I doing something wrong? I encountered this issue when trying to get the buildbot-gitea plugin to work, since it requires either treq or txrequests, and installing treq pulls in the same package dependencies that buildbot[tls] does. Fortunately, installing txrequests does not pull those packages in, so if I use txrequests instead I can get buildbot-gitea to work. However, it seems odd that MailNotifier should break in this way just because those additional packages have been installed.

Thanks in advance for any suggestions...