Open Cart email deliverability issue fix needed (opencart)

I have an opencart 1.5.4 site. Symptoms: E-mails from my opencart application to my admin email address are not delivered (for example: sending message through website contact form not work). Whereas website e-mails are still usually delivered to third party email addresses (order update, reminder e-mails for customers). I use sendinblue for email service and it has been working properly. Sendinblue shows almost zero bounce rate. Logs show: that all emails are all delivered and opened, which is a contradiction. This can mean that when sender and recipient is the same, they are filtered by my email client, Gmail. Other issue: my new customers get emails into their promotion or spam folder, not inbox. So email deliverability should be improved by improving email content. Your task is the following: ===================== - improve email deliverability to customers (reminders, order emails) - resolve the undelivered/lost administrator emails problem Note: Bids around or below 75 usd are preferred. Emails were never optimized therefore it's an easy task to improve them. PLEASE NOTE: OPENCART EMAIL SENDING WORKS (TESTED). THIS JOB IS ABOUT IMPROVE EMAIL DELIVERY IN BOTH TASKS. :)