Outlook issue with sending iCalendar meeting invitation with additional (not .ics) attachment

Question

I need to send meeting invitations that sometimes can include .pdf attachments. So i'm building System.Net.Mail.MailMessage with Alternative view (for iCalendar content), with Body and with an attachment if it exists. I need that most popular mail clients (that support calendars) be able deal with my invitation emails.

Here is my code that is pretty working for:

gmail (web/mobile app) with/without pdf attachment
yahoo mail (web/mobile app) with/without pdf attachment
outlook (desktop) without pdf attachment only

    public virtual MailMessage CreateMailMessage(string content, Meeting meeting)
    {
        MailMessage mailMessage = new MailMessage();
        mailMessage.From = _mailsAddressesProvider.GetFromEmaiMailAddress(meeting);
        mailMessage.To.AddRange(_mailsAddressesProvider.GetToEmaiMailAddresses(meeting));
        mailMessage.CC.AddRange(_mailsAddressesProvider.GetCCEmailAddresses(meeting));
        mailMessage.Bcc.AddRange(_mailsAddressesProvider.GetBCCEmailAddresses(meeting));

        mailMessage.Subject = GetMessageSubject(meeting);
        mailMessage.Body = GetMessageBody(meeting);
        mailMessage.IsBodyHtml = IsBodyHtml();

        ContentType contentType = new ContentType("text/calendar");
        contentType.Parameters.Add("method", Method);
        contentType.Parameters.Add("name", AttachmentName);
        AlternateView avCal = AlternateView.CreateAlternateViewFromString(content, contentType);
        mailMessage.AlternateViews.Add(avCal);

        AddAttachments(mailMessage, meeting);

        return mailMessage;
    }

    public virtual bool AddAttachments(MailMessage mailMessage, Meeting meeting)
    {
        byte[] meetingMaterialsBytes = _meetingMaterialsRepository.GetMeetingMaterails(meeting);
        if (meetingMaterialsBytes == null || meetingMaterialsBytes.Length == 0)
        {
            return false;
        }
        ContentType contentType = new ContentType(MediaTypeNames.Application.Pdf);
        Attachment attach = new Attachment(new MemoryStream(meetingMaterialsBytes), contentType);
        attach.ContentDisposition.FileName = "MeetingMaterials.pdf";
        attach.ContentDisposition.Inline = true;
        attach.ContentDisposition.DispositionType = DispositionTypeNames.Inline;
        attach.ContentId = "MeetingMaterials";

        mailMessage.Attachments.Add(attach);
        return true;
    }

So the issue is when email with attachment is being opened in Outlook.

Here is how such an email is opened in Outlook without pdf attachment - OK:

Here is how such an email is opened in Outlook with pdf attachment - OK: Probably there is no issue with iCalendar (ics) content but with System.Net.Mail.MailMessage object.

So the problem is that I need Outlook to open an email with attachment as a meeting invitation but not as a ordinary email.

Any suggestions about what can be wrong with my MailMessage parts? Thanks in advance.

Dmitry Streblechenko Dmitry Streblechenko · Accepted Answer · 2015-07-16T20:03:13

There were quite a few similar questions. You need to make sure the MIME structure of your message is right.

See for example Outlook 2013 invite not showing embeded attachment - text/calendar;method=REQUEST

Outlook issue with sending iCalendar meeting invitation with additional (not .ics) attachment

1 Answers