I’m trying to send a calendar invite using a Java service. The email is sent appropriately, however, the calendar invite is received as an attachment in the form of a .ics file. However, rather than having to click on the file to view the invite information, I’d like to send it as a meeting invitation that includes accept/reject options.

Below is my code; I am unable to find my mistake. Please assist me!

public String sendCalendarInvite(MailDetails mailDetails) {
        try {
            JavaMailSenderImpl mailSender = setMailConfig();
            MimeMessage mimeMessage = mailSender.createMimeMessage();
            String toEmail = mailDetails.getToEmail();
            mimeMessage.setRecipients(MimeMessage.RecipientType.TO, toAddresses.toArray(new InternetAddress[0]));
            String subject = mailDetails.getSubject();
            String from = mailDetails.getFromEmail();
            String startTime = mailDetails.getStartTime();
            String endTime = mailDetails.getEndTime();
            String mailBody = mailDetails.getMailBody();
            String contentType = mailDetails.getContentType();
            mimeMessage.setFrom(new InternetAddress(from));
            mimeMessage.setSubject(subject);
            mimeMessage.addHeaderLine("method=REQUEST");
            mimeMessage.addHeaderLine("component=VEVENT");
            StringBuilder buffer = new StringBuilder();
            buffer.append("BEGIN:VCALENDARn" +
                           "METHOD:REQUESTn" +
                           "PRODID:Microsoft Exchange Server 2010n" +
                           "VERSION:2.0n" +
                           "BEGIN:VTIMEZONEn" +
                           "TZID:Asia/Kolkatan" +
                           "END:VTIMEZONEn" +
                           "BEGIN:VEVENTn" +
                           "ATTENDEE;ROLE=REQ-PARTICIPANT;RSVP=TRUE:MAILTO:" + toEmail + "n" +
                           "ORGANIZER;CN=Foo:MAILTO:" + from + "n" +
                           "DESCRIPTION;LANGUAGE=en-US:" + mailBody + "n" +
                           "UID:"+UUID.randomUUID()+"n" +
                           "SUMMARY;LANGUAGE=en-US:Discussionn" +
                           "DTSTART:" + startTime + "n" +
                           "DTEND:" + endTime + "n" +
                           "CLASS:PUBLICn" +
                           "PRIORITY:5n" +
                           "DTSTAMP:20200922T105302Zn" +
                           "TRANSP:OPAQUEn" +
                           "STATUS:CONFIRMEDn" +
                           "SEQUENCE:$sequenceNumbern" +
                           "LOCATION;LANGUAGE=en-US:Microsoft Teams Meetingn" +
                           "BEGIN:VALARMn" +
                           "DESCRIPTION:REMINDERn" +
                           "TRIGGER;RELATED=START:-PT15Mn" +
                           "ACTION:DISPLAYn" +
                           "END:VALARMn" +
                           "END:VEVENTn" +
                           "END:VCALENDAR");

//             Create the message part
            MimeBodyPart calendarEventBodyPart = new MimeBodyPart();
            // Create first body part for calendar event
            calendarEventBodyPart.setHeader("Content-Class", "urn:content-classes:calendarmessage");
            calendarEventBodyPart.setHeader("Content-ID", "calendar_message");
            calendarEventBodyPart.setDataHandler(new DataHandler(
                    new ByteArrayDataSource( buffer.toString(), "text/calendar;method=REQUEST")));
//             Create a Multipart
            MimeMultipart multipart = new MimeMultipart("alternative");
            multipart.addBodyPart(calendarEventBodyPart);
            mimeMessage.setContent(multipart);
            mimeMessage.setReplyTo(new InternetAddress[]{new InternetAddress(Q_DL)});
            mimeMessage.setSentDate(new Date());
            mimeMessage.saveChanges();
            logger.info("Sending mail ");
            logger.info("mail id: {}", mimeMessage.getMessageID());
            mailSender.send(mimeMessage);
            logger.info("Calendar invite sent successfully");
            return "Calendar invite Sent Successfully.";

        } catch (AddressException e) {
            throw new CustomRuntimeException("Address Exception during sending mail :" + e.getMessage());
        } catch (MessagingException e) {
            throw new CustomRuntimeException("Messaging Exception during sending mail: " + e.getMessage());
        } catch (Exception e) {
            throw new CustomRuntimeException("Exception during sending mail: " + e.getMessage());
        }
    }

I am trying to send a outlook calendar invite but it is received as an attachment.