问题
This example of mail sender works well Send Email Multiple Upload Form & Attachment File
but, problem is what every email sending ONLY to yahoo emails, forwarding to spam folder.
Why? How to prevent sending mail to spam folder?
回答1:
From DKIM.ORG:
DKIM enables a mechanism that permits potential email signers to publish information about their email signing practices; this will permit email receivers to make additional assessments about messages. DKIM's authentication of email identity can assist in the global control of "spam" and "phishing".
Its one of the possibilities that Yahoo! might marked the email as spam because the message is not signed with DKIM signature when is sent "DKIM defines a domain-level digital signature authentication framework for email".
There are also another headers that Yahoo! might mark them as spam.
[1] http://www.dkim.org/specs/rfc5585.html
来源：https://stackoverflow.com/questions/14672137/yahoo-emails-forwarding-to-spam-folder