When sending mail or using exinext to test mail, you are unable to connect to an external mail server with error -27: failed to expand helo_data: System iconv failed.
Exim fails to expand the file /etc/mailhelo file due to a icon or image. This is unable to open and utilize the "�" character causing Exim to not send out mail. For example, an entry such as "*:�myfqd.madeupdomain.tld" would prevent the file from being expanded and read properly.
When the file fails to expand, it's usually from wrong permissions or incorrect formatting. Seeing System iconv failed indicates there is an image or an invalid character present in the mailhelo. Removing this entry in /etc/mailhelo and clear the retry database will resolve this.
Clear Exim Retry DB to bypass "retry time not reached" after fixing an issue with delivery