Email Issue

my store encounter email issue after upgrade to 4.5.1
my order notification email fail to sent to customer, but successfully sent to order department and vendor. only send notify email to customer having issue, prompt out error
ErrorMessage could not be sent.
Mailer Error: SMTP Error: data not accepted.SMTP server error: DATA END command failed Detail: Relaying disallowed as Stark Industries SMTP code: 553
anyone please help me, im have no clue what happen to my store, send notify to order department and vendor successful without error, only send to customer having error even my customer email is valid.
i try install clean version 4.5.1, still having the same issue.
Thank You

i think its everybodys have the same problem after upgrade. i upgrade 4.4.2 to 4.4.2sp2 i get this error too.

The error is from the end user (your customer). Most likely an authentication issue.


my email work fine on 4.4.2 SP, but upgrade to 4.5.1, having this issue occur. i dont know what exactly happen? i test to send newsletter with same smtp setting, it works find, i send notify to order dept and vendor work fine. only the customer notify email having error. i have use the same customer and i able to send him newsletter.

anyone facing this issue?

Thank You

Some code is crash when upgrade i think. because its working before upgrade