Email Test Working but failed to send documents


I have started to use Offline Manager to test how it is working and could we use it in the business. I have an issue with emails at the moment. I have added email information in settings and all is good test email went ahead ok and received. But when I tried to send a sales order by email from Manager the following set of errors have came up and can’t figure out how to fix it. Can you please help with the following errors?

System.Net.Mail.SmtpException: System.Net.Mail.SmtpException: 454 4.7.0 Too many login attempts, please try again later. i93sm14862225wri.57 - gsmtp
at System.Net.Mail.SmtpClient.CheckStatus (System.Net.Mail.SmtpClient+SmtpResponse status, System.Int32 i) [0x0001a] in :0
at System.Net.Mail.SmtpClient.Authenticate (System.String user, System.String password) [0x00065] in :0
at System.Net.Mail.SmtpClient.Authenticate () [0x000b1] in :0
at System.Net.Mail.SmtpClient.SendCore (System.Net.Mail.MailMessage message) [0x00132] in :0
at System.Net.Mail.SmtpClient.SendInternal (System.Net.Mail.MailMessage message) [0x00050] in :0
at System.Net.Mail.SmtpClient.Send (System.Net.Mail.MailMessage message) [0x00091] in :0
at ManagerServer.HttpHandlers.Businesses.Business.Email.Post () [0x005a3] in <84e3f085e8e8413babf5fd833e86f931>:0