Checklist: What Can Cause Email Bounces

Dis­patching an email does not gua­ran­tee recep­ti­on. When an email has been sent but not deli­ver­ed, we speak of a “boun­ce”. The goal of email mar­ke­ting is to keep the boun­ce rate (pro­por­ti­on of boun­ces in the num­ber of tar­ge­ted email addres­ses) as low as pos­si­ble. Howe­ver, boun­ces can have many rea­sons, which each requi­re a dif­fe­rent cour­se of actions.

If a dis­patched email can­not be deli­ver­ed, it is cal­led a boun­ce. Preven­ting boun­ces is an import­ant task in email mar­ke­ting. Howe­ver, to effi­ci­ent­ly take action again­st boun­ces, you must know their poten­ti­al cau­ses. The rea­sons for boun­ces are mani­fold and not each boun­ce requi­res action.

1. Inbox Full

When a recipient’s inbox is full, no fur­ther emails can be deli­ver­ed. The boun­ce mes­sa­ge in this case con­ta­ins a line, such as recipient’s inbox is full. All rele­vant email cli­ents noti­fy their user, when the inbox is full. As soon as the reci­pi­ent clears his inbox, the boun­ce rea­son is remo­ved and the email can be deli­ver­ed. Tem­pora­ry boun­ces are often cal­led soft boun­ces. When an inbox is too full over a lon­ger time peri­od, you can assu­me that the account is no lon­ger used. If emails per­man­ent­ly can­not be deli­ver­ed, we are spea­king of hard boun­ces. In this case, the reci­pi­ent should be dele­ted from the mai­ling list.

2. Absence

If a reci­pi­ent is absent for a lon­ger peri­od, e.g. due to ill­ness, he can con­fi­gu­re the email out-of-office assis­tant so that inco­m­ing emails will not be deli­ver­ed. In most cases, this should be obvious from the auto­ma­ti­cal­ly sent absen­ce mes­sa­ge. The cau­se for the boun­ce usual­ly cor­rects its­elf when the reci­pi­ent returns, i.e. the out-of-office assis­tant is deac­tiva­ted.

3. Email Loop

The email loop can best be explai­ned by means of an exam­ple. Let’s assu­me that a reci­pi­ent goes on holi­day and con­fi­gu­res his absen­ce assis­tant to for­ward emails to ano­ther reci­pi­ent. This reci­pi­ent, howe­ver, is also absent and has set his absen­ce assis­tant for­wards to the first reci­pi­ent. The crea­ted loop will con­ti­nuous­ly send emails from one inbox to the other. Most email ser­vers howe­ver, are able to iden­ti­fy an email loop and inter­rupt it  as long as they are cor­rect­ly con­fi­gu­red. A pos­si­ble boun­ce mes­sa­ge for an email loop would be mail loop: too many hops (too many ‘Recei­ved:’ hea­der fiel­ds).

4. Address Does Not Exist

Emails can only be deli­ver­ed to addres­ses which exist. A boun­ce due to a non-exis­tent address can be iden­ti­fied, for exam­ple through a line, such as “reci­pi­ent email address unk­nown”. In this case, you should check, whe­ther the email address has been cor­rect­ly ent­e­red into the mai­ling list. If addres­ses were manu­al­ly cap­tu­red, the­re could be a typo. If the reci­pi­ent him­self has made a mis­ta­ke, e.g. “John.Smiht@xyz.cim ins­tead of” you can­not cor­rect the address your­self. When an address does not exist (any­mo­re), you can dele­te it from the mai­ling list.

5. Email Has Been Filtered

The­re is the pos­si­bi­li­ty that an email has been fil­te­red by the recipient’s email ser­ver. This can have dif­fe­rent cau­ses, which unfor­t­u­n­a­te­ly, are not always obvious from the boun­ce mes­sa­ge. The most com­mon cau­se is that the email has been clas­si­fied as SPAM and the pos­si­ble mes­sa­ge would read: “Email was iden­ti­fied as spam”.

6. Problems With The Email Server

Mes­sa­ges such as error wri­ting mes­sa­ge or mes­sa­ge could not be stored indi­ca­te a fault with the recipient’s email ser­ver.