"Mailbox size limit exceeded" when sending mails on an empty exchange account with MailKit .Net - vb.net

Question

I am using MimeKit and Mailkit to send emails from my VB.NET application, through my own SMTP server (run on Windows Server 2016, with SmarterMail).
Until then, I was sending emails to info#mywebsite.com which is an alias of infos#mywebsite.com and it worked very well. This email account is a exchange account with more of 49 Gio free.
Since a few days, I've received this error : Mailbox size limit exceeded
When a set a spy on it, this is what I get :
This is the log :
S: 235 Authentication successful
C: MAIL FROM:<info1#mywebsite.com> SIZE=599
S: 250 OK <info1#mywebsite.com> Sender ok
C: RCPT TO:<info#mywebsite.com>
S: 452 <info#mywebsite.com> Mailbox size limit exceeded
C: RSET
S: 250 OK
I don't understand why I get this error while my recipient account is pretty much empty.
When I try to send email from my outlook account to info#mywebsite, I get no error.
When I try to send emails from my code to anothers recipients, I get no error.
My disk space is very large on my mail serveur (almost 2 To).
This is my code :
Dim message As New MimeMessage()
message.From.Add(New MailboxAddress("My website", "info1#mywebsite.com"))
message.To.Add(New MailboxAddress("My website", "info#mywebsite.com"))
message.Subject = "any subject"
Dim builder As New BodyBuilder()
builder.TextBody = textemail
builder.HtmlBody = htmlemail
message.Body = builder.ToMessageBody()
' SERVER SMTP
Using client As New MailKit.Net.Smtp.SmtpClient()
client.ServerCertificateValidationCallback = (Function(sender, certificate, chain, sslPolicyErrors) True)
client.Connect("mail.mysmtpserver.com", 587, MailKit.Security.SecureSocketOptions.None)
client.Authenticate("Mailkit_SMTP_UserName", "Mailkit_SMTP_Password")
client.Send(message)
client.Disconnect(True)
End Using
Thanks a lot for any suggestion (I don't find any related topic on Google)

Answer 1

I've found what was wrong in my SMTP server : Smartermail has it own mailbox size configuration for any mail account, that is limited at 100Mb.
You can change it by going on : your domain > Manage > Account