Manager will not email statements and invoices

See below for what I get both when I try to email statements and invoices from within Manager. This problem showed up today after updating to 19.6.66. Please advise how to fix. Thank you.

ELR Engineering - Invoice 876 - Trep Development, LLC ul, ol { padding-left: 10px }.float-left { float: left !important; }.float-right { float: right !important; }.text-align-left { text-align: left !important; }.text-align-right { text-align: right !important; }div.content { background-color: #fff; padding: 30px; box-shadow: 0px 0px 5px #ccc; border: 1px solid #ccc; width: auto }a.file-close:hover { color: #999; }#sidenav div { padding: 0px; background-color: #fafafa; box-shadow: inset 1px 1px 0px #fff; }#sidenav img { opacity: 0.4; vertical-align: top; width: 16px; height: 16px }#sidenav .tab-active { background-color: #fff; border-right: none }#sidenav, #sidenav { line-height: 16px; display: block; position: relative; white-space: nowrap; padding: 12px; font-size: 11px; font-weight: bold; font-family: ‘Lucida Grande’,Verdana,sans-serif }#sidenav table { border: 1px solid #ccc; border-top: none; border-spacing: 0px; width: 100% }#sidenav .tab-active table { border-right: 1px solid #fff }#sidenav a:hover { text-decoration: none }#sidenav a:hover img { opacity: 0.6 }#sidenav .tab-active img { opacity: 0.6 }#sidenav span.count { background-color: #FFFFFF; border: 1px solid #CCCCCC; border-radius: 3px 3px 3px 3px; color: #666666; font-size: 10px; font-weight: bold; padding: 3px 6px; }#sidenav span.count-zero { border: 1px solid #EEEEEE; color: #DDDDDD }#sidenav { margin-left: 10px; }#sidenav a:hover span.tooltiptext { visibility: visible }.tooltiptext { visibility: hidden; background-color: #000; color: #fff; text-align: center; padding: 5px 10px; border-radius: 6px; position: absolute; z-index: 99999; top: 7px; left: 42px; }.tooltiptext::after { content: ’ '; position: absolute; top: 50%; right: 100%; margin-top: -5px; border-width: 5px; border-style: solid; border-color: transparent black transparent transparent; }a#feedback-link { color: #ccc; padding: 3px 6px; margin-left: 5px; border: 1px solid #ccc; border-radius: 3px }a#feedback-link:hover { text-decoration: none; background-color: #fff; color: #333; border: 1px solid #999; text-shadow: none }@media print { body { -webkit-print-color-adjust: exact !important; } }

System.Net.Mail.SmtpException: System.Net.Mail.SmtpException: Syntax error, command unrecognized. The server response was: 5.7.0 Mailgun is not loving your login or password
at System.Net.Mail.RecipientCommand.CheckResponse(SmtpStatusCode statusCode, String response)
at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at ManagerServer.HttpHandlers.Businesses.Business.Email.Post()

Please search the forum before starting new topics. This has nothing to do with your software update. There is a problem with the third-party email service used by Manager when you are not using a custom SMTP setup.