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ISP filters incoming emails and auto deletes email when the TO address is different from the actual recipient mailbox address...   

Can I use a
non-existing REPLY TO email address to send messages?

Sending or broadcasting emails with a fake or non-existing REPLY TO email address usually result in bounced or undeliverable emails.

Because most ISPs mail server have requirements for outgoing or return REPLY TO email addresses as well as performing

a reverse nslookup--to prevent and disallow you to send email to another ISPs SMTP mail server, when the sender or recipient is a non-local user.

This feature was implemented

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to protect the mail server from being used by spammers to relay their messages by using another company’s network and computer resources. See: Blacklist
551 User not local, please try <forward-path> or Invalid Address: Relay request denied
(to view a list of error return codes)

RFC delivery status notification indicates that the recipient's email address has changed and your ISP mail server is forwarding it back to you and/or your ISP SMTP mail server does not accept email when neither the sender nor the recipient is a non local user.

Non-local user ISPs mail server, to prevent relaying of emails or SPAM will not allow you to send emails that is outside your domain--meaning that; the FROM or (REPLY TO) using an email address domain that is different from the log-in domain address.

Many ISP filters incoming emails and automatically delete mails where the TO address are different from the actual recipient address-delete not bounced-hence you won't know if the message actually got to the intended recipient.
Email Filtering

nslookup a DNS whois tool that perform forward and reverse DNS queries for the current domain address (to get an IP address of a hostname and hostname of the IP address).

Whois a tool to contact network registries to find out contact information for the current domain or IP address.

Traceroute tool, finds the route packets take between you and the selected address

Dig tool, requests all the DNS records for a host or domain



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If you are using your own mail server program. See: Mail Server FAQs

For more information listed below: see Email FAQs Glossary

Mail readers, Mailbox, User Agent,
ARP Address Resolution Protocol
NAT Network Address Translation
MAC Media Access Control MAC Address
MTA Message Transfer Agent
Traceroute tool - finds the route packets
Finger program for retrieving Internet user info
Dig tool requests all DNS records for a host/domain
SMTP Relay Verify (checking) tool
Ping Packets Internet Groper
Whois a tool to contact network
nslookup a DNS whois tool that perform forward/reverse DNS queries for a domain
Telnet - A program that allows a user to remotely login
Throughput, MaxMtu, UART, RWIN, MSS,
TTL-Time To Live
ICMP - Internet Control Message Protocol
RFC - Request For Comments
SMTP - Simple Mail Transport Protocol
SMTP return error codes lists
Winsock Error Codes
Port Numbers, Router, Server-time-out,
Mail Host, Mail server, Email gateway
FTP - File Transfer Protocol
UDP - User Datagram Protocol



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