====== Helo command rejected: Host not found: retry timeout exceeded  ======
Email tidak bisa terkirim ke alamat tertentu dan saya mendapatkan error seperti ini 
<code>
agratxxx@wahanakarsa.co.id
host mail.wahanakarsa.co.id [150.107.149.228]
SMTP error from remote mail server after RCPT
TO:<agraxxxx@wahanakarsa.co.id>:
450 4.7.1 <server1.ph.gs>: Helo command rejected:
Host not found: retry timeout exceeded
hajxxxx@wahanakarsa.co.id
host mail.wahanakarsa.co.id [150.107.149.228]
SMTP error from remote mail server after RCPT
TO:<hajxxxxx@wahanakarsa.co.id>:
450 4.7.1 <server1.ph.gs>: Helo command rejected:
Host not found: retry timeout exceeded
rikxxxxxx@wahanakarsa.co.id
host mail.wahanakarsa.co.id [150.107.149.228]
SMTP error from remote mail server after RCPT
TO:<rikxxxxx@wahanakarsa.co.id>:
450 4.7.1 <server1.ph.gs>: Helo command rejected:
Host not found: retry timeout exceeded
</code>

Kesimpulan yang diambil dari baris berikut ini ** <server1.ph.gs>: Helo command rejected:
Host not found: retry timeout exceeded** Artinya hostname tidak bisa diakses dari luar.

====== Cara Pengujian ======
Ping server1.ph.gs dari komputer anda atau dari jaringan lain. Jika tidak bisa di ping maka itulah penyebab errornya.

====== Solusi ======
Ubah setting dns dan pointing server1.ph.gs ke ip server email tsb.