I am using same account at multiple times in 'To' section like this ( oMail.To = new AddressCollection("abc.xyz.com,abc.xyz.com,abc.xyz.com");)
Now when I send email then only one mail sent to abc.xyz.com.
I want to send three mails on this account
How can I achieve this functionality?

could you generate a log file with LogFileName property and paste here?

Please hide your password/user in the log file.

Log file data :

Tue, 11 Mar 2014 16:29:59 +0530
Resolving server ...
Server: smtp.gmail.com
Port: 25
ConnectType: ConnectSSLAuto
Protocol: SMTP
AuthType: AuthAuto
User: XXXXXXXXXXX
Alias:
Drafts: drafts
Password: XXXXXXXXXXX
EHLO: False
HeloDomain: enbraun-5.domain
MailFrom:
SocksProxyServer:
SocksProxyPort: 1080
SocksProxyUser:
SocksProxyPassword:
ProxyProtocol: Socks5

Create socket InterNetwork,Stream,Tcp ...
Start to connecting ...
74.125.129.109, 25
Connected

220 mx.google.com ESMTP vb7sm73252606pbc.13 - gsmtp
EHLO enbraun-5.domain
250-mx.google.com at your service, [122.176.45.8]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250 CHUNKING
STARTTLS
220 2.0.0 Ready to start TLS
EHLO enbraun-5.domain
250-mx.google.com at your service, [122.176.45.8]
250-SIZE 35882577
250-8BITMIME
250-AUTH LOGIN PLAIN XOAUTH XOAUTH2 PLAIN-CLIENTTOKEN
250-ENHANCEDSTATUSCODES
250 CHUNKING
AUTH LOGIN
334 VXNlcm5hbWU6
YXNodS5zYWp3YW4zODVAZ21haWwuY29t
334 UGFzc3dvcmQ6
YXNodSMxMjM=
235 2.7.0 Accepted
MAIL FROM:
250 2.1.0 OK vb7sm73252606pbc.13 - gsmtp
RCPT TO:
250 2.1.5 OK vb7sm73252606pbc.13 - gsmtp
RCPT TO:
250 2.1.5 OK, duplicate recipients will be consolidated. vb7sm73252606pbc.13 - gsmtp
RCPT TO:
250 2.1.5 OK, duplicate recipients will be consolidated. vb7sm73252606pbc.13 - gsmtp
DATA
354 Go ahead vb7sm73252606pbc.13 - gsmtp
[Data Stream: 1851]

.
250 2.0.0 OK 1394535608 vb7sm73252606pbc.13 - gsmtp
Quit
221 2.0.0 closing connection vb7sm73252606pbc.13 - gsmtp


As per this log file your dll consolidate duplicate recipients.
how we can overcome this issue?

It is consolidated by server, because you send the same email to 3 same recipients, most server consolidate it.

You can try to send email to different recipients in one email, the server will not consolidate it.