Hey! It's hard to give you a good answer without some more information. How are you using Sendgrid, via the API or their SMTP relay? Could you provide a code snippet?

@asb I'm using SMTP relay. It is a form where users will enter email address and some other information and after submission, a mail will be sent to that email address with some attachments. This is a working version of that application - http://www.aan-nahl.com/test/tanvir/ibeacon-tool/
Do I need to install curl seperately or does it come with php bundle?

The PHP cURL module is not installed by default. On an Ubuntu system, you can install it with sudo apt-get install php5-curl

Is it possible to get a list of steps, from start to finish? Here is my attempt:

Option #1
Insert the following html form into the index.html file
Create another page, emails.html to display the incoming messages.
The Parse API posts the parsed email to the url of this new page.

To set up the Parse API to forward incoming email to this new webpage:
(SendGrid's Parse API lets your app accept incoming email and perform some operation on the content.)

Create a Digital Ocean account and droplet
Log in to your server domain
Go to the DNS settings
Create a new record - MX
Set the TO section to mx.sendgrid.net

Create a SendGrid account
Go to the Parse Settings page on https://app.sendgrid.com/settings/parse
Click the green "Add Host & URL" button
Under hostname, enter mydomain.com
Under URL enter the URL http://mydomain.com/emails
Select "Spam Check" if desired
Select "Send Raw" to receive a raw message

*Option #2:
*Change to your mail config directory:
cd /etc/mail
Make a auth subdirectory
mkdir auth
chmod 700 auth #maybe not, because I cannot apply cmd "cd auth" if I do so.

Create a file with your auth information to the smtp server
cd auth
touch client-info

In the file, put the following, matching up to your smtp server:
AuthInfo:your.isp.net "U:root" "I:user" "P:password"

Generate the Authentication database, make both files readable only by root
makemap hash client-info < client-info
chmod 600 client-info
cd ..

Add the following lines to sendmail.mc. Make sure you update your smtp server The first single quote for each string should be changed to a backtick (`) like this:
define(SMARTHOST',your.isp.net')dnl
define(confAUTHMECHANISMS',EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE(authinfo',hash /etc/mail/auth/client-info')dnl

run
sudo sendmailconfig

When you typed in sudo sendmailconfig, you should have been prompted to configure sendmail.

For reference, the files that are updated during configuration are located at the following (in case you want to update them manually):

/etc/mail/sendmail.conf
/etc/cron.d/sendmail
/etc/mail/sendmail.mc

You can test sendmail to see if it is properly configured and setup by typing the following into the command line:

$ echo "My test email being sent from sendmail" | /usr/sbin/sendmail myemail@domain.com