Re: [exim] syntactically invalid argument(s) - rejected HELO

Igor Robul wrote:

> Marc Perkel wrote:
>
>> I have a customer who is getting real email from korea (yes - there
>> is email that isn't spam) . But - getting this in the logs.
>>
>> syntactically invalid argument(s)
>>
>> What does this mean?
>>
> Does host name in HELO contain underscore? We have one Vietnamese
> client who has '_ ' in HELO.
> Put
> helo_allow_chars = _
> in your exim configuration file.
>
Yes - I think that's it! So - why is an underscore a reason for rejection?