Failure to send a password reset email should not 500

[alexmv]

The password reset form calls send_email synchronously:

zulip/zerver/forms.py

Lines 347 to 376 in e7c62c4

	if user is not None:
	context["active_account_in_realm"] = True
	context["reset_url"] = generate_password_reset_url(user, token_generator)
	send_email(
	"zerver/emails/password_reset",
	to_user_ids=[user.id],
	from_name=FromAddress.security_email_from_name(user_profile=user),
	from_address=FromAddress.tokenized_no_reply_address(),
	context=context,
	realm=realm,
	request=request,
	)
	else:
	context["active_account_in_realm"] = False
	active_accounts_in_other_realms = UserProfile.objects.filter(
	delivery_email__iexact=email, is_active=True
	)
	if active_accounts_in_other_realms:
	context["active_accounts_in_other_realms"] = active_accounts_in_other_realms
	language = request.LANGUAGE_CODE
	send_email(
	"zerver/emails/password_reset",
	to_emails=[email],
	from_name=FromAddress.security_email_from_name(language=language),
	from_address=FromAddress.tokenized_no_reply_address(),
	language=language,
	context=context,
	realm=realm,
	request=request,
	)

This means that if that emails fails to send, it raises an EmailNotDeliveredException:

zulip/zerver/lib/send_email.py

Lines 262 to 282 in e7c62c4

	try:
	# This will call .open() for us, which is a no-op if it's already open;
	# it will only call .close() if it was not open to begin with
	if connection.send_messages([mail]) == 0:
	logger.error("Unknown error sending %s email to %s", template, mail.to)
	raise EmailNotDeliveredException
	except smtplib.SMTPResponseException as e:
	logger.exception(
	"Error sending %s email to %s with error code %s: %s",
	template,
	mail.to,
	e.smtp_code,
	e.smtp_error,
	stack_info=True,
	)
	raise EmailNotDeliveredException
	except smtplib.SMTPException as e:
	logger.exception(
	"Error sending %s email to %s: %s", template, mail.to, str(e), stack_info=True
	)
	raise EmailNotDeliveredException

We should catch those in the password reset form, and display a message that says something like:

Something went wrong sending an email to that address. Double-check that you typed it correctly, and try again in a few minutes!

[zulipbot]

Hello @zulip/server-development members, this issue was labeled with the "area: emails" label, so you may want to check it out!

[timabbott]

Hmm, I'm not sure what precise semantics we want here. I think if the failure indicates that the server is unable to send outgoing emails at all, we do want a 500 error. (One thing to consider is that the signup/password reset flows are often where self-hosted administrators might be when they are first trying to get email working).

So we perhaps want the behavior to depend on what type of exception we get when trying to send the email?

[alexmv]

SMTP error codes are an unregulated mess, which makes them very hard to act on. For instance, a failure we recently saw in production was:

454 Temporary service failure

...and code 454 is technically a transient failure of the receiver system, which is accurate here. But it's also used for declining to relay mail or needing authentication and those are just the first two hits that turn up on Google.

[alexmv]

This also applies to send_confirm_registration_email, which is also synchronous, and can lead to a 500.