I can't recieve any verification emails.

Can you start by telling me what kind of SMTP service you are using (eg.. Windows 2000 Virtual SMTP)

Also, do the following from a command line:

from another network (friend, work, etc..)
nslookup -type=mx yourdomain.com

you will receive a list of mx records

Telnet via port 25 into the host with the lowest cost

example: telnet yourhost.yourdomain.com 25

if you connect, attempt to send a test message to one of your recipients.

Example:

Helo yourworkdomain.com
mail from: you@yourworkemail.com
rcpt to: you@yourdomain.com
data
subject: test
.
 and see if you recieve the message.

I don't don' what kind od STMP service my hosting company using.

When I type nslookup -type=mx mydomain.com ;

D:\>nslookup -type=mx mydomain.com

Non-authoritative answer:
mydomain.com     MX preference = 10, mail exchanger = smtp.secureserver.net
mydomain.com     MX preference = 50, mail exchanger = mailstore1.secureserver.net


smtp.secureserver.net   internet address = xx.xxx.xxx.xxx

I coulldn't connect via telnet.

You have e-mail hosting by a company - so you use their POP or IMAP server for getting your mail, right?
You can receive mail that friends send to you, to the address you use on the hosting company, which means that the reception of mails (done by the hosting company's server) works OK and the POP/IMAP service works, since you can get your mail from the server.

If you don't get mail from some senders, you must find out:
1) Did they indeed send a mail.
2) Did they use the correct address (your return address, most likely)
3) Are they blocked by your hosting company (originating domain on blacklist or so)

If they do send mails, with the correct address and you still don't get anything from them, you'll have to talk to your hosting company, so they can examine their logs, or talk to a sender, to find out if they get a bounce.
/RID

I do all the things you said before and Ip addresses are not in the blacklist.

If my assumptions about your setup were correct, this is exceedingly odd. It seems to boil down to some senders not getting their mail through. Without knowledge about what happens to these messages, further digging is difficult. An examination of the server logs is called for. Since these would be in the hands of your hosting company, I suggest you ask them if they can help with a check for missing mails. Or, if some of your friends has got a bounce when sending to you, ask if they can send you the mail headers and error message.
/RID

Revenade,

I'd like to revisit my original comment.  It seems odd that only your friends can send to you.  Also, you mentioned that you could not telnet via port 25 into your primary mx.

Do your friends use the same ISP that you do?
did you perform your telnet test as follows: telnet yourhost.yourdomain.com 25
where yourhost.yourdomain.com is actually the host with the least cost when you do an nslookup.

Thanks

 I am using a University LAN. My mail system works normally except verification mails. I can receive e-mails from my friends (even outside of my country) and even some mailing lists which don’t require verification mails. The problem which drives me crazy about a month is able to get verification mails. I told the problem to my hosting company but they insist on to send them bounced e-mails. But I don't know how to do it.

 I try to connect via telnet by;
Telnet myhost.mydomain.com 25
I got The following lines;

220 smtpout-1-1d.secureserver.net ESMTP
HELO mydomain.com
250 smtpout-1-1d.secureserver.net
mail from mydomain.com
250 Sender accepted.
rcpt to: user@mydomain.com
553 Sorry, that domain isn't in my list of allowed rcpthosts.

Revenade,

When you say "verification emails" are you talking about delivery receipts and read receipts?  If so, some organizations don't allow deliver receipts from the internet because of the risk of looping messages.

Just to clarify:  You receive email just fine from any source, but you don't always get delivery and read receipts, correct?

 For instance, if you subscribe a mailing list, they send you a e-amil to verify your mail address. That is the type of e-mail which I am not able to get.

 I sent mail from the record mx10 but could not accomplish a telnet connection with the other one.