SQL Server and SMTP Issue in C#

problem1: If multiple agents are sending emails to multiple users at the same time, then the email of one agent is getting inserted into the other.

for exp: Agent Amit send email to user alex and agent shiva send email to user aman then after send email only agent shiva logs [Which Agent has sent the email to which user] will be created for both user alex and aman.

Hope you will understand.

---Below is the procedure

CREATE PROCEDURE [dbo].[Get_SendEmailSendTOPAX_CS_V1]

    @PAXUID Varchar(250),
    @AgentName Varchar(250)
AS
BEGIN
    SET NOCOUNT ON;
    SET TRANSACTION ISOLATION LEVEL SERIALIZABLE

    BEGIN TRANSACTION;

    if EXISTS(select 1 from [dbo].[tbl_agent] where agentgalaxyname=@AgentName AND Isactive=1)
    BEGIn

        IF OBJECT_ID('#SendEmailPAX_CS', 'U') IS NOT NULL
        DROP TABLE #SendEmailPAX_CS;

        --DROP TABLE IF EXISTS dbo.#SendEmailPAX_CS;

Create table #SendEmailPAX_CS
(
    PAXUID Varchar(250),
    AgentName Varchar(250),
    BookingID INT,
    BookingTypeID INT,
    AgentID INT ,
    Gateway_Type nvarchar(250),
    Gateway_Type_Name nvarchar(250),
    Gateway_Email nvarchar(250),
    AirlineName nvarchar(250),
    Gateway nvarchar(250),
    TollFreeNumber nvarchar(250),
    Subject_TFN varchar(50),
    ConsentURL_ varchar(50) ,
    GatewayID INT ,
    PAX_Email varchar(50),
    PAXEmailSend_ID INT,
    EMail_Subject varchar(250),
    FinalGateway varchar(250)
)

INSERt INTO #SendEmailPAX_CS (PAXUID,AgentName)
SELeCT @PAXUID,@AgentName

UPDATE SEP
SET SEP.AgentID = TA.AgentID
from #SendEmailPAX_CS SEP
INNER JOIN tbl_Agent TA
ON TA.AgentGalaxyName=@AgentName

UPDATE SEP
SET SEP.BookingID = TPD.PassengerDetailID , BookingTypeID=TPD.BookingTypeID
from #SendEmailPAX_CS SEP
INNER JOIN tbl_PassengerDetail TPD
ON TPD.PassengerUID=@PAXUID

UPDATE #SendEmailPAX_CS
SET Gateway_Type = APD.Gateway_Type,Gateway_Type_Name=APD.Gateway_Type_Name,PAX_Email=APD.PAX_Email,
FinalGateway=(
    case
    when #SendEmailPAX_CS.Gateway_Type='Everyware' THEN 'SFC'
    when #SendEmailPAX_CS.BookingTypeID in (4,1023,1025) THEN 'Cancellation'
    ELSE APD.Gateway_Type end)
    FROM (SELECT TOP 1 SUBSTRING(gateway,0, CHARINDEX('-',gateway)) [Gateway_Type],Gateway [Gateway_Type_Name] ,PAX_Email,PNR FROM [dbo].tbl_AuthorizePaymentDetails
    where pnr=(select cast(BookingID as varchar) from #SendEmailPAX_CS where PAXUID=@PAXUID) ORDER BY ID DESC) AS APD
    WHERE #SendEmailPAX_CS.BookingID = APD.PNR;


UPDATE #SendEmailPAX_CS
SEt Gateway_Email=MGT.Gateway_Email,Gateway=MGT.Gateway,TollFreeNumber=MGT.TollFreeNumber,AirlineName=MGT.AirlineName,Subject_TFN=MGT.Subject_TFN,
ConsentURL_=MGT.ConsentURL
from (select top 1 Gateway_Email [Gateway_Email],TravelName [Gateway], AirlineName [AirlineName],
REPLACE(REPLACE(TollFreeNumber, CHAR(13), ''), CHAR(10), '') [TollFreeNumber],
REPLACE(REPLACE(Subject_TFN, CHAR(13), ''), CHAR(10), '')[Subject_TFN],ConsentURL[ConsentURL]
from [dbo].tbl_ManageGateway where Gateway_type=(Select top 1 FinalGateway from #SendEmailPAX_CS where PAXUID=@PAXUID)) AS MGT


Select PAXUID,AgentName,BookingID,BookingTypeID,AgentID,Gateway_Type,Gateway_Type_Name,
Gateway_Email,AirlineName,Gateway,
TollFreeNumber,Subject_TFN,ConsentURL_,
GatewayID,PAX_Email ,
PAXEmailSend_ID ,
EMail_Subject ,
FinalGateway from #SendEmailPAX_CS where PAXUID=@PAXUID

    DROP TABLE #SendEmailPAX_CS
    END
    COMMIT TRANSACTION;

END