E-Mails are not received

Hi @Jason_beth,

• Have you done any modifications recently in the mail reader configuration?  
• Did you notice any error message or warning with the emails which were not received? 
• Further did any ‘Delivery failed’ message has been received by the party who have sent the email? https://support.office.com/en-us/article/sent-email-in-outlook-com-comes-back-delivery-failed-45e048ac-f7b1-4c0f-b525-081cb34f1062
• Could you please check whether the information in the below link will address the same issue you are facing? https://www.outlook-apps.com/outlook-not-sending-email-stuck/

Hi @Sandun,
Thank you for the reply. No recent modification done in the mail reader. Neither error, nor warning messages were appearing for the emails which were received by the IFS. Further, I didn’t get any Delivery failed receipts for the emails which were not received to IFS. I followed your URLs. But seems the issue, not same in the Links.
It’s hard to say the title length exceeds 200 characters. We have requested from our suppliers to follow a common standard when sending emails. Based on the supplier details length can be varied.

Seems the issue is being occurred when sending emails to IFS only. 
We asked our suppliers to use a format when sending emails. We maintain a format similar to below. But not the exact one. So subject length can be exceed 200 characters as per the below example. 
Ex:
Company : XXXXXXXXX : Description : Confirmation of Material details : Product Chemical : T0009-93333-44454-XA334453 : Date : 29-December-2019 : Officer : V-02564 : Approved : V-02313 : Count : 35 : Remain : N/A : Advanced payment : Paid : END