Setting mail.smtp.connectiontimeout longens requests when working with office 365 - spring-boot

Question

We are sending mails in an email service with org.springframework.mail.javamail.JavaMailSender via an office 365 account and SMTP and set the following parameters in application.yml:
spring:
mail:
host: ${EMAIL_HOST:smtp.office365.com}
port: ${EMAIL_PORT:587}
username: ${EMAIL_USERNAME}
password: ${EMAIL_PASSWORD}
properties:
mail:
smtp:
auth: true
connectiontimeout: 5000
timeout: 5000
writetimeout: 5000
starttls:
enable: true
socketFactory:
port: 465
class: javax.net.ssl.SSLSocketFactory
The strange thing is: if we set the connectiontimeout to 5s, the service gets a response after 5s. If we set it to 20s, the o365 responds after 20s.
My expectation is that <connectiontimeout> is the maximum amount of time, that the sending may take and not the actual time.
Funny thing is that when setting another provider than office365, connectiontimeout works as expected.
Does anyone have this issue as well and maybe know how to solve that?
Our sender service:
#PostMapping
#ResponseStatus(HttpStatus.ACCEPTED)
public void sendMail(#RequestHeader(name = "X-API-KEY", required = true) String requestApiKey, #Valid #RequestBody EmailSendRequest email, HttpServletResponse response) {
if(!apiKey.equals(requestApiKey)){
LOGGER.error("Unauthorized api key" + requestApiKey);
throw new ResponseStatusException(HttpStatus.UNAUTHORIZED);
}
try {
LOGGER.info("Received request to send mail Subject=[{}] To=[{}] From=[{}]", email.getSubject(), email.getTo(), email.getFrom());
MimeMessage message = mailSender.createMimeMessage();
message.setFrom(new InternetAddress(email.getFrom().getEmail()));
message.addRecipients(Message.RecipientType.TO, toAddressArray(email.getTo()));
message.addRecipients(Message.RecipientType.CC, toAddressArray(email.getCc()));
message.addRecipients(Message.RecipientType.BCC, toAddressArray(email.getBcc()));
message.setSubject(email.getSubject());
message.setSentDate(new Date());
Multipart multipart = new MimeMultipart();
MimeBodyPart messageText = new MimeBodyPart();
messageText.setContent(email.getContent().getValue(),
email.getContent().getType() == null ? DEFAULT_CONTENT_MIMETYPE : email.getContent().getType());
multipart.addBodyPart(messageText);
addAttachments(multipart, email.getAttachments());
message.setContent(multipart);
if(message.getRecipients(Message.RecipientType.TO) != null ||
message.getRecipients(Message.RecipientType.CC) != null ||
message.getRecipients(Message.RecipientType.BCC) != null)
{
mailSender.send(message);
}
else {
LOGGER.warn("Email not send! No recipients or all ignored.");
response.setHeader("X-Ignored","true");
}
LOGGER.info("Mail Subject=[{}] To=[{}}] From=[{}] successfully sent.",email.getSubject(),email.getTo(),email.getFrom());
} catch (MessagingException e) {
LOGGER.error("Error sending mail Subject=[{}] To=[{}] From=[{}]:", email.getSubject(), email.getTo(), email.getFrom(), e);
throw new ResponseStatusException(HttpStatus.INTERNAL_SERVER_ERROR);
} catch (MailSendException mailSendException) {
Exception[] exceptions = mailSendException.getMessageExceptions();
for (Exception e : exceptions){
if (e instanceof SMTPSendFailedException && (((SMTPSendFailedException)e).getReturnCode() == 554)){
LOGGER.error("Error sending mail Subject=[{}] To=[{}] From=[{}]: This sender mail address is not allowed.", email.getSubject(), email.getTo(), email.getFrom());
throw new ResponseStatusException(HttpStatus.FORBIDDEN);
}
}
LOGGER.error("Error sending mail Subject=[{}] To=[{}] From=[{}]:", email.getSubject(), email.getTo(), email.getFrom(), mailSendException);
throw new ResponseStatusException(HttpStatus.INTERNAL_SERVER_ERROR);
} catch (MailAuthenticationException e) {
LOGGER.error("Error sending mail Subject=[{}] To=[{}] From=[{}]: Wrong SMTP login credentials provided. \nMSG:{}", email.getSubject(), email.getTo(), email.getFrom(),e.getMessage());
throw new ResponseStatusException(HttpStatus.NETWORK_AUTHENTICATION_REQUIRED);
}
}

Answer 1

It seems, that the SocketFactory was responsible for this behaviour. Removing the following lines from application.yml makes the application work as expected:
socketFactory:
port: 465
class: javax.net.ssl.SSLSocketFactory