An asynchronous call is already in progress

SMTP it’s not implemented properly probably. I cannot send two messages simultaneously.

 Unexpected Server Exception:
System.InvalidOperationException: An asynchronous call is already in progress. It must be completed or canceled before you can call this method.
   at System.Net.Mail.SmtpClient.SendAsync(MailMessage message, Object userToken)
   at FluentEmail.Smtp.SendMailEx.SendMailExImplAsync(SmtpClient client, MailMessage message, CancellationToken token)
   at FluentEmail.Smtp.SmtpSender.SendAsync(IFluentEmail email, Nullable`1 token)
   at FluentEmail.Core.Email.SendAsync(Nullable`1 token)

Take a look here: https://stackoverflow.com/questions/50036795/getting-error-while-sending-bulk-email-an-asynchronous-call-is-already-in-progr

[Yukon]

I have found the cause of the issue to be the SmtpClient is reused throughout the entire lifetime of the application. A fix can be made in applications without pulling my patch by explicitly using the function version of AddSmtpSender. For example AddSmtpSender(() => new SmtpClient("smtp.example.com", 25)) instead of AddSmtpSender("smtp.example.com", 25).

[NickVandenberghe]

For example AddSmtpSender(() => new SmtpClient(“smtp.example.com”, 25)) instead of AddSmtpSender(“smtp.example.com”, 25).

I already fixed this now. I configured a smtpclient before adding it to the AddSmtpSender function I fixed my error by configuring the smtpclient in the AddSmtpSender function