TLS fails to authorise if the server stopped supporting HELO command

[qnikst]

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Yandex smtp server dropped support of the HELO command in the protocol as a result authorisation fail with log:

HaskellNet-SSL RECV: "220 sas1-37da021029ee.qloud-c.yandex.net SMTP\r"
HaskellNet-SSL SEND: "HELO Alexanders-MacBook-Pro.local\r\n"
HaskellNet-SSL RECV: "502 5.5.1 Unrecognized command\r"
)

If we don't try to send HELO , and sent EHLO immediately everything works fine:

openssl s_client -connect smtp.yandex.ru:465
220 iva8-a4a480c9f089.qloud-c.yandex.net SMTP
EHLO alexander.vershilov.localhost
250-8BITMIME
250-PIPELINING
250-SIZE 42991616
250-STARTTLS
250-AUTH LOGIN PLAIN XOAUTH2
250-DSN
250 ENHANCEDSTATUSCODES

There are two options to fix this issue:

1. drop support of the old servers that can't work with HELO
2. do not fail if the server returns 502 on HELO command.

I think that the second option is better and will try to provide a MR soon.